There is an advanced course for experienced lip-readers who want to become intructors. If they qualify, they will teach lip-reading classes themselves.

All the participants in this course-for-instructors have excellent sight, hearing and other senses. They are all high-level lip-readers. They are all currently in good health and in top form.

Today a group (lets say 26 - it's not important) of them are sitting in a circle facing inwards. It's a clear sunny day and everyone is in view of everyone else.

Their instructor explains the process and they start.

Person A turns to person B and, hiding their face from all but B, silently mouths a single word, for example "hippopotamus", or any other word. In the same fashion, B mouths what they guess the word is to C and so on, all around the circle.

Finally person Z mouths their guess to A then asks out loud, "Was that your word?"

Person A truthfully replies out loud, "I haven't the slightest idea!"

Everyone laughs then they turn to the instructor for feedback.

The instructor says "Any questions? No? Excellent, you all pass that exercise! Let's move on.


Please explain the purpose of the exercise and give a convincing reason why they passed. Optionally can you say something that is likely true about the location where this class took place?


  1. They are all speaking the same language and they are all fluent native speakers of that language. Arbitrarily I'll say that the language is British English because that is where I'm from, but it could some other normal, spoken language.

  2. Everyone has an excellent memory.

  3. No-one is drunk or otherwise incapacitated.

  4. (added) You can assume that the original word is easy to lip-read correctly for these people.


3 Answers 3


One possibility is that

the word A gave was one that was ambiguous with lip-reading, and the point of this exercise was to teach that there are ambiguities that cannot be sorted out that way. For instance, the words "bet" and "pet" are identical when mouthed; if A said one of them, and saw Z mouth it, they would not know which of the two words was Z's.

If Z said something obviously wrong, A would've said "no"; the message did make it around the chain, so they all passed.

  • 1
    $\begingroup$ That's not my answer. Remember that these people are all first-class lip-readers. A said, "I haven't the slightest idea!". If this had been an ambiguous word, A would have said something like "It's close" or "It could be". Take it that A literally doesn't have the slightest idea - not even an iota. $\endgroup$ Commented Aug 15, 2020 at 18:37

Because of

COVID-19. They all wear masks.

Obviously the exercise is nonsense in this context.
But it could be that this exercise is mandatory in the cursus. So they oblige.

PS: it doesn't really explain how A can ignore what word he himself mouthed. I would say the instructor gave the word and was masked too. So A doesn't know what word he was supposed to transmit.

For the people to genuinely pass, that would mean the instructor was masked, the participants were not, A didn't know the word to transmit so he mouthed "I haven't the slightest idea!", which was correctly passed around.

The test is a success because the instructor saw what A mouthed and saw that this longer sentence was transmitted correctly. One problem is that A never actually lip-read anything, but that is the fault of the instructor.

  • $\begingroup$ Your first statement is correct although rot13(bayl bar crefba zhfg unir jbea n znfx. Jub?). This simple exercise was done only once and was not pointless. Can you say why, based on other information in the question? Why did they genuinely pass? $\endgroup$ Commented Aug 15, 2020 at 19:28
  • $\begingroup$ rot12(U paz'f dqmp daf13.) $\endgroup$
    – Florian F
    Commented Aug 15, 2020 at 19:39
  • $\begingroup$ @FlorianF rot12(fch9(wty19(Mooadpuzs fa tffbe://daf13.oay/ kagd yqeemsq etagxp mofgmxxk nq daf14. Mzp ftmf'e itk qhqdkazq geq daf13.))) $\endgroup$
    – WhatsUp
    Commented Aug 16, 2020 at 2:52
  • $\begingroup$ Sorry but your logic is faulty in a couple of places. For example, A knows A's word. Also A followed the rule to utter a single word. $\endgroup$ Commented Aug 16, 2020 at 9:08
  • $\begingroup$ My first solution (before the PS) is faulty. I updated the answer to propose an explanation why the single-word rule was broken and why it is still a success. I added another paragraph for clarity. $\endgroup$
    – Florian F
    Commented Aug 16, 2020 at 10:45

Is it because:

The sun was in his eyes, so he could not see Z's face at all, just a silhouette.

This would make the purpose of the session:

Be aware of your position relative to the sun when communicating outside.

A few comments

The riddle clearly says that this lesson took place on a clear, sunny day. When Z mouths the word to A, everyone has already had their turn, so perhaps Z and A do not feel the need to hide their faces which could have incidentally blocked the sun. Z would need to have the sun directly behind him, so that it is shining right into A's eyes.

They passed because:

They effectively demonstrated the purpose of the lesson - everyone is reminded to be aware of their visibility.

What does this tell us about their location?

Well, obviously they were outside, and for the level of sunstrike required to fully block communication the sun would probably have to be quite low on the horizon which means that the location was either quite flat all around or elevated without buildings or hills to block out the sun. It could have been near sunrise or sunset or it could have been during winter in a location nearish either of the poles where the sun would have stayed low all day.


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