Just had a really nasty idea for a computer game...

It's your standard room-escape game, of the sort Tomatea and Tesshi-e do so well. There's a chest of four drawers, with a different kind of code required for each. The second drawer down requires a numeric code. There are also a couple of other numeric codes scattered around the place.

Here's the nasty bit: There are no clues whatsoever for the second drawer. Which is fine, because it's empty. However, it is unlocked by taking the key to the main door. So if you finish the game, think "But what about that drawer? I can't have solved it and forgotten!" and go to check...

(I got the idea from a game I thought had done this, when I had actually solved it and forgotten.)