Below is a puzzle I have come across on two different occasions, the latest one being when reading the introduction to Gary Drescher’s book “Good and Real: Demystifying Paradoxes from Physics to Ethics” (which I did not come close to finishing due to boredom, although I may return to it). Based on the amount of exposure I get to puzzles and brainteasers, I’d expect to have come across this one more than twice, as it is a good one. You need no special education at all to understand the question, so no one can claim exemption due to their major or specialty in life!
Puzzle: Why does a mirror reverse the left and right directions, but not the up and down directions? (In other words: Your mirror image wears his watch on his right hand. Why doesn’t he wear his shoes on his head?)
No monetary reward for the solution to this one, as there is (still unclaimed!) for the last one.
Update Tues 7pm: Recommended way of answering: post the answer in the comments, but in a foreign language (ideally one with an alphabet different from English’s), in order to allow readers to browse the comments, and decipher only the answers they’re interested in (you can use an online translator both to encode and to decipher the answers).
Update Thurs 11am: Spoilers in comments