I remember this very old riddle involving lateral thinking. I was surprised that I cannot find it here. (Or maybe did I use wrong keywords? If so, please mark as duplicate)

Girl is looking at an object.
During the flow of the time, it is becoming thinner at one side and thicker at another. What is she looking at?

In addition, it has multiple solutions. Can you guess them all? I will give some hints.

  1. Is today classic (and at the same time it is the most exact solution).

  2. Is today vintage.

  3. Is today medieval technology (or even possibly neolithic).

2 and 3 can be difficult because nowadays, most of young people have never seen such devices. Luckily 1 is still in use today.


*4. Writing this, I just noticed another solution on my screen.

Edit 2:

As many people post very good solutions I noticed that I should be more specific:
Hint 2:

1 and 2 are kinds of medium.
3 is a tool.
4 can be a part of UI component

Ultimate Edit:

I just removed unnecessary history from the question
Congratulations to xhienne and FLash.

  • 2
    $\begingroup$ Not sure if one of the answers you are looking for is rot13(tynff), but if it is that has actually been disproved. $\endgroup$ – lPlant Sep 25 '18 at 20:20
  • $\begingroup$ @lPlant I am afraid it is not. $\endgroup$ – mpasko256 Sep 26 '18 at 8:38
  • $\begingroup$ Please see my discussion with xhienne $\endgroup$ – mpasko256 Sep 27 '18 at 16:01

Since correct answers have already been given for 2 and 4, here is my proposal for 3:

Is it a spindle?
Or a spinning wheel?

[edit] And here is my proposal for 1:

She is just reading a book

To sum it up:

1 => book
2 => audio cassette
3 => spindle
4 => progress bar

  • $\begingroup$ Bingo! Congratulations! ;) $\endgroup$ – mpasko256 Sep 26 '18 at 17:04
  • 1
    $\begingroup$ 1 -there is still missing solution for it. user477343 was only close. $\endgroup$ – mpasko256 Sep 26 '18 at 17:14
  • $\begingroup$ I didn't see FLash's edit made in meantime: He is very very close to solution now. $\endgroup$ – mpasko256 Sep 26 '18 at 17:28
  • $\begingroup$ Bingo! Congratulations! $\endgroup$ – mpasko256 Sep 27 '18 at 8:40
  • $\begingroup$ Thanks @mpasko256 Flash has an equal number of good answers and their answer for word 1 was very very close (and as valid as a book). I suggest you ask Flash to correct their answer for word 1, to add the answer for word 3 and that you accept their answer instead of mine. $\endgroup$ – xhienne Sep 27 '18 at 10:11

I think the classic answer (I’ve never heard this one before) might be a


This is because

She herself is getting thinner in some places, and thicker in others?

Another answer might be

An Hourglass?


The width of the sands get thinner at the top and thicker at the bottom

Another answer might be

A Lit Candle?


It gets thinner at the top but the wax pools at the bottom

  • $\begingroup$ It is not a solution but very good shots at all! +1 $\endgroup$ – mpasko256 Sep 25 '18 at 15:20
  • $\begingroup$ The second answer here was my first thought; however, self-winding is another good option. $\endgroup$ – Taco タコス Sep 25 '18 at 15:22
  • 1
    $\begingroup$ HAHA Stole it from me as I was posting lol $\endgroup$ – Taco タコス Sep 25 '18 at 15:26
  • 1
    $\begingroup$ Close one @PerpetualJ!! $\endgroup$ – El-Guest Sep 25 '18 at 15:26

I see some possibilities


Audio Tape or Cassette enter image description here


A Scroll for writing? enter image description here


Progress bar. The width of the green increases as white decreases. enter image description here Or Scroll bar?

  • $\begingroup$ Congratulations: Your 1 is bingo for my 2! Your 2: Somebody just said that but it is not a solution. 4: close enough but not yet $\endgroup$ – mpasko256 Sep 26 '18 at 8:36
  • $\begingroup$ 4: After edit: Bingo! $\endgroup$ – mpasko256 Sep 26 '18 at 9:28
  • $\begingroup$ Oh, I didn't see your edit for 1. in the meantime. You are so close with it now! Just remember the hint that it is something still in use today ;) $\endgroup$ – mpasko256 Sep 26 '18 at 17:24

Just a couple thoughts:


Sundial; a sundial casts a shadow that gets thicker over time (at certain angles).


Candle Clock; candle clock is an obvious choice because it slowly becomes thin at the top and thicker at the bottom as the wax melts.


Could the classic answer be

Her own writing from a pencil?


At first, the pencil could have been sharpened, so the lines in her written letters were thin. Then over time, the lead in the pencil would have slowly become blunt and her letters consequently looked thicker and bolder. Since she might be writing from left to right, the left side (or page) might look thinner than the right.


She might be sharpening a pencil.


A pencil is at first just a stick of lead inside some wood, and then gets thinner on the side it is sharpened whilst having the same thickness on the other side. The other side might even have a rubber at the end which gets slightly thicker the more you rub with it.

If the girl was

writing in cursive (which can be considered feminine)

then there would be some kind of "flow".

  • 1
    $\begingroup$ You are very close but not yet! :) It is something very similar $\endgroup$ – mpasko256 Sep 26 '18 at 8:37

I heard once that

Glass is some kind of superfluid, so over time, as noticable in old windows, the glass falls down with gravity, so the window is thicker at the bottom than at the top.


I've since heard that that isn't true, and the reason the window is thicker at the bottom in old windows is simple down to how they were made back then.

  • $\begingroup$ I suppose that @lPlant had it already in mind. But interesting way of thinking anyway! $\endgroup$ – mpasko256 Sep 26 '18 at 9:31
  • $\begingroup$ @mpasko256 oh sorry, i looked through other answers to see if anyone had already said it but must have missed that comment $\endgroup$ – AHKieran Sep 26 '18 at 9:44

I think the answer is



during the flow of the time (maybe a hint here), the amount of sand in the upper part decreases (so the sand pile becomes "thinner"), but it increases in the lower part (becomes "thicker")


it's actually very old technology, however not yet neolithic


The hourglass symbol can be seen on a screen as a cursor icon!

  • 1
    $\begingroup$ El-Guest just proposed this solution but unfortunately it is not an answer. $\endgroup$ – mpasko256 Sep 26 '18 at 11:09

Is it:

the moon? Over time (say a month or longer), the moon waxes and wanes, changing it's appearance from thin to thick.


For the first one, I thought about...

her own life, that is thiner on the future side, and thicker on the past one!

For the second one,

the candle sounds obvious

For the third, I thinkg PerpetualJ first answer matches!


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