A police investigator walks into a room. He sees two dead bodies on the floor, those of the unfortunate duo Alice and Bob, the players in many physics thought experiments. They had been locked in the room together. The investigator notices several things:

  • The door was sealed, and remained sealed since Alice and Bob were locked in one day before.
  • There is a broken window high up on the wall, with shattered pieces of glass all over the floor. The investigator finds that it is impossible to reach. The window was not broken when Alice and Bob were locked in. There are no other exits besides this window and the door.
  • There is a table by the window approximately four feet in height. Even an unlucky fall wouldn't have killed a person.
  • Security camera footage shows that nobody - living or dead - entered or exited the room. No inanimate objects entered or exited the room, either (obviously, things like light and air would have passed through the broken window). The footage is accurate.
  • There is a glass on the table, which has also been broken. It appears that it was a glass of water, because water was spilled all over the floor.
  • There is nothing else in the room - including no weapons.
  • Alice and Bob's bodies appear unharmed. There are no traces of poison.
  • Prior to being locked in the room, Alice and Bob had everything they needed to survive - food, water, oxygen, etc.
  • Alice and Bob died before the investigator opened the door.

The investigator relates all this information to his supervisor. The supervisor cannot solve the puzzle, yet the investigator, smiling, says that he knows the answer.

How did Alice and Bob die?

Note: This isn't a riddle of my own devising. A friend of mine got it from somewhere, and related it to me.

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    $\begingroup$ If Alice and Bob turn out to be cats or fish, I have a few questions about what department my tax dollars are funding. $\endgroup$ – FraserOfSmeg Mar 4 '16 at 4:52
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    $\begingroup$ @JGreenwell As a follow-on, was the inspector's name Schrödinger? $\endgroup$ – Hugh Meyers Mar 4 '16 at 8:45
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    $\begingroup$ I'm not sure of the "how", but I'm pretty sure I know the "who". It was Mallory. Don't believe me? Ask Eve. She always seems to know what's going on between those two... $\endgroup$ – Parthian Shot Mar 4 '16 at 15:00
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    $\begingroup$ They were mayflies, which have a lifespan of one day. The broken glass is inconsequential. $\endgroup$ – MackTuesday Mar 4 '16 at 17:39
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    $\begingroup$ They actually left a detailed description of what was going on, but sadly in addition to physics, Alice and Bob were master cryptographers and no one could figure out what the message said... $\endgroup$ – corsiKa Mar 4 '16 at 19:23

16 Answers 16


Alice and Bob...

...are actually fish! They were in a glass fishbowl on the table that had shattered, perhaps due to an unfortunate resonant frequency*. This frequency also broke the glass window. This explains the broken glass and water on the floor, and the two dead (but otherwise uninjured) fish :(


For completeness sake I'm gonna say that a passing ambulance was blasting a siren at said resonant frequency.

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    $\begingroup$ But how could fish be those "players in many physics thought experiments"? I'd really like to see fish deal cards or write numbers on a board! And then logically... no, Thor seems much more likely a reason ;) $\endgroup$ – Paul Evans Mar 4 '16 at 2:18
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    $\begingroup$ I as a taxpayer want to know why police investigators investigate dead fish to that level of thoroughness. $\endgroup$ – Joshua Mar 4 '16 at 5:02
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    $\begingroup$ @Joshua: Normally, you'd be right but in this case, the Chief Constable believed there was something fishy. $\endgroup$ – Magoo Mar 4 '16 at 5:26
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    $\begingroup$ @Joshua What can I say, they were really carp at their job. $\endgroup$ – AZGreenTea Mar 4 '16 at 5:51
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    $\begingroup$ What's worse is that the supervisor couldn't solve the conundrum of the dead fish on the floor $\endgroup$ – mowwwalker Mar 4 '16 at 7:36

We are asking the wrong question:

* The security tapes show that nobody else entered the room, and we are told that the inspector is the one to have unsealed the door.
* We are told everything which was in the room, and there was no method of communication that could have been used by Alice or Bob to have summoned the police themselves.
* So the most important question is: since nobody found the bodies, and since Alice and Bob could not have summoned the police themselves, why was the investigator even there, unsealing the door?

The only rational answer to this critical conundrum ("why was the inspector there?") is that the inspector must have already known the bodies were there to be found.

And therefore..

The investigator must have killed Alice and Bob some number of days in the past, and then sealed their bodies into the room in order to conceal his crime, and then returned to "discover" their bodies the next day.

Critically, note that the puzzle never actually specifies that Alice and Bob were alive at the time of being sealed into the room. Since we've established that they died at some point before the inspector unsealed the door, and that nobody killed them while they were sealed inside the room, the only logical conclusion is that they had died at some point before even being sealed into the room in the first place.

As a result, the investigator gets away with his shocking crime, and gets to smile enigmatically as he informs his supervisor that he knows how it happened. And then invite him out to dinner, and maybe back to his place for afters. Maybe his supervisor would finally notice him now!

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    $\begingroup$ Sometimes I feel like lateral-thinking is the fanfic of puzzles. :) $\endgroup$ – Trevor Powell Mar 4 '16 at 6:56
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    $\begingroup$ We have definitely passed into the fanfic zone on this one. This is quite an old puzzle and I am sure many other experienced puzzlers on this site share my fond memories of struggling through this and similar puzzles in our childhoods. Consider these answers as a tribute to an old friend. $\endgroup$ – Hugh Meyers Mar 4 '16 at 13:50
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    $\begingroup$ The "inside job" conclusion is the best conclusion, and I applaud it wherever I find it. Was it an accident I was overcharged for that muffin, or was it... CONSPIRACY? $\endgroup$ – Parthian Shot Mar 4 '16 at 15:05

The investigator knew, as the supervisor did not that

The room was not heated!


There was a sudden, catastrophic cold snap the night before.
The extreme cold caused the metal window frame to contract, breaking the glass.
The water in a sealed glass container froze, breaking it.
When temperatures returned to normal in the morning, the ice melted.
Therefore, Alice and Bob died of hypothermia. I know this is the right answer because OP cleverly hid the word "ice" in Alice's name. The remaining letters are an anagram of BLABO, an oil tank cleaning system described here.
This is the last piece of the puzzle. Clearly, the reason the room wasn't heated was because the oil tank for the furnace was being cleaned with BLABO.
And the investigator smiled at this tragedy. That sick, sadistic so and so!

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    $\begingroup$ I so wanted this to be correct. $\endgroup$ – Max Li Aug 27 '16 at 18:33

They were killed by:



They both had their hands on the glass of water (probably due some complicated competition of a mathematical nature) and at the exact moment water poured out of the glass and onto the floor in a continuous steam forming a perfect circuit to ground - a bolt from Thor (who may of been a bit jealous) crashed through the window! Ever so lightly zapping them into another dimension.

The investigator knows because:

He is Thor (working in his day job)

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    $\begingroup$ Creative, although not what I'm going for. Would someone struck by lightning show evidence of being struck, though? $\endgroup$ – HDE 226868 Mar 4 '16 at 1:43
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    $\begingroup$ Hmmmm, got me there. Suppose even Thor couldn't have zapped them that lightly if he had to smash through a window to get them. $\endgroup$ – Paul Evans Mar 4 '16 at 1:47
  • $\begingroup$ Or Mjölnir just crushed the window? $\endgroup$ – Falco Mar 7 '16 at 13:01
  • $\begingroup$ @Falco Of course! The old double whammy... take out the window with Mjölnir and then zap Alice and Bob with just enough juice to finish them off but leaving no trace. And Thor can do this so quickly, between security camera frame snaps even. $\endgroup$ – Paul Evans Mar 7 '16 at 15:14
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    $\begingroup$ I wish this was asked by @Randal'Thor ... that would be ironic... $\endgroup$ – Omega Krypton Feb 8 '19 at 11:51

Alice and Bob



there was no oxygen in the room to begin with. "Prior to being locked in the room, Alice and Bob had everything they needed to survive - food, water, oxygen, etc." Presumably the air was vacuumed out after the room was sealed. The investigator opening the door caused air pressure to rapidly equalize, breaking the glass and the window.

  • $\begingroup$ If it was a complete vacuum, the door would have been impossible for the investigator to open, given the atmospheric pressure on it from the outside $\endgroup$ – mowwwalker Mar 4 '16 at 8:06
  • $\begingroup$ Next to that, their bodies would have exploded during the vacuuming. $\endgroup$ – Stephan Bijzitter Mar 4 '16 at 8:23
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    $\begingroup$ @mowwwalker If the door opens outwards, sure it's nigh impossible to open, but if it opens inward, all it basically needs is for someone to nudge the handle down and the air pressure will fling it open. $\endgroup$ – Robin James Kerrison Mar 4 '16 at 10:54
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    $\begingroup$ @RobinJamesKerrison You're right, and the doors to locked rooms always open inwards in order to keep the hinges on the inside of the room. $\endgroup$ – Probst Mar 4 '16 at 20:23
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    $\begingroup$ @StephanBijzitter Why is it hard to believe, and why would you expect it to explode? Too many movies for you, I think. In any event Wikipedia has a halfway decent article on the matter: en.wikipedia.org/wiki/Space_exposure $\endgroup$ – corsiKa Mar 5 '16 at 19:23

Unbeknownst to anyone there was a large block of dry ice in the room. It sublimates so fast that it filled the room with CO2 suffocating Alice and Bob. One of them had a glass of water which slipped from their hands to the floor. The extra pressure caused the window to break open.

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    $\begingroup$ Wouldn't the glass of the broken window be outside, not inside? $\endgroup$ – Erics Mar 4 '16 at 3:04
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    $\begingroup$ Glass always falls both ways $\endgroup$ – Dr Xorile Mar 4 '16 at 3:20
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    $\begingroup$ @Dr Xorile No, it depends on where the pressure is added. $\endgroup$ – Scott Mar 4 '16 at 4:59
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    $\begingroup$ So you're saying that I was wasting my time wearing goggles when working with evacuated glass tubes? Because the glass would only have gone inwards? :-) Brittle materials tend to have material going all directions when they fail. I agree that the majority of the glass would probably have been outside, but I wouldn't be shocked to find some glass inside. $\endgroup$ – Dr Xorile Mar 4 '16 at 16:52
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    $\begingroup$ A variant on this: Someone threw the dry ice in through the window, that's why it's broken. $\endgroup$ – Loren Pechtel Mar 4 '16 at 19:02

The room was pumped with carbon monoxide prior to Alice and Bob being locked in. They don't notice at first, but start to feel light headed and decide to throw the glass of water at the window to get some air. It's unfortunately too little too late and there isn't enough time for the carbon monoxide to fully disperse before Alice and Bob are killed by carbon monoxide poisoning.


Alice and Bob both suffered from a chronic condition that required them to take pills twice a day. They had taken with them into the room a glass of water for that purpose. At the beginning of their stay inside the locked room, Alice dozed off and Bob decided to scare her and wake her up. When Alice woke up, she was so startled that she screamed at just the right pitch to shatter both the window and the glass of water. Having lost the water they needed for their pills, they both died within hours.


I'd think this one would be obvious.

Outside the window was another small enclosed space, containing a fan. The fan was blowing SO HARD that it broke the window and knocked the glass of water over. Alice and Bob were unfortunate victims of fan death. When in doubt... Fan death.

Alternative answer to the question "How did Alice and Bob die?":


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    $\begingroup$ I'd like my fanfic with double fanfic! $\endgroup$ – raven Mar 4 '16 at 17:48

Alice and Bob were trying to Science the Shit out of some hydrazine to create water for growing potatoes.

Unfortunately they forgot about the Oxygen they were breathing out and blew themselves up.

Take that Neil Armstrong!


Alice and Bob were performing physics experiments. There is a chance of fire in the room and must have produced lots of smoke and they would have started suffocating can't use oxygen because it will ignite fire more tried to break the window using the glass but it was too late for them, enough carbon was inside their lungs to suffocate them and they died.


The "room" is a submarine.

When the exterior pressure got too high during a descent, the high window shattered inward and the submarine flooded, causing both Alice and Bob to drown (and incidentally breaking an otherwise unrelated Crimson Flounderâ„¢-brand drinking glass that happened to be present). The flooding also accounts for the water on the floor. (In fact, there was rather a lot of water on the floor. And almost everywhere else.)

The room being a submarine also explains why the room would contain a supply of food and water, why there are no weapons to hand, and why the room would even be sealed in the first place.

Presumably the inspector accidentally discovered the remains of the room (and thereby the bodies of Alice and Bob) while engaging in some scuba training, in an effort to gain some impressive new skills which would cause his dreamy (but frustratingly tsundere) supervisor to finally notice him.


Alice and Bob are / were fish and were in the glass of water. A bird saw them or for other reasons flew into the window and broke it. A piece of glass dropped and knocked the glass off the table and on to the floor thus dislodging the fish from the water and hence asphyxiating them.

  • $\begingroup$ Then the glass wouldn't be on the table, would it now? But I agree with your basic premise. $\endgroup$ – Wildcard Mar 4 '16 at 19:56
  • $\begingroup$ The glass may not have been knocked off the table, just over so the fish could flow and flop out. $\endgroup$ – HankCa Mar 5 '16 at 2:17
  • $\begingroup$ @HankCa if bird broke the glass when it saw them, wouldn't it also eat them and leave no bodies ? $\endgroup$ – georoot Mar 6 '16 at 12:48
  • $\begingroup$ The window was high and it broke it but didn't fly through. $\endgroup$ – HankCa Mar 7 '16 at 21:17
  • $\begingroup$ @HankCa Because it was a small window. $\endgroup$ – wizzwizz4 Apr 15 '18 at 15:29

Perhaps there was a downpour of rain, and the two drowned?


There was a sound so horrible it killed Bob, Alice, the window, and glass of water.

  • $\begingroup$ It killed the window? $\endgroup$ – merrybot May 3 '20 at 1:52
  • $\begingroup$ @merrybot Indeed $\endgroup$ – haykam May 3 '20 at 1:53
  • $\begingroup$ But windows aren't alive to begin with so they can't be killed. They simply exist. $\endgroup$ – merrybot May 3 '20 at 1:55
  • $\begingroup$ Or do I not know something about window biology? $\endgroup$ – merrybot May 3 '20 at 1:55

Alice and Bob's last work assignment was participating at a physics experiment at CERN, and unbeknownst to them,

a tiny black hole had gotten stuck in Bob's throat.

It slowly grew, until Bob sneezed. The extra velocity and the glass of water it hit caused it to grow rapidly, sucking out all the air in the room. Unfortunately Alice and Bob suffocated before the window burst in.

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    $\begingroup$ That's... not how black holes work. At all. $\endgroup$ – Deusovi Mar 4 '16 at 20:33
  • $\begingroup$ I second that. Black holes just suck up stuff. $\endgroup$ – merrybot May 3 '20 at 1:52

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