I will reveal the answer, because it seems this riddle has more than one, so it's not that good after all. The answer I know is: coffin, but we can agree that poison is also logical.
Here's next one, more lateral. Officially it is an anecdote coming from Warsaw University Physics Department and it started to be popular sometime in the 60ies or 70ies, but it may not be true. Anyway.
Student takes a verbal exam. Professor, visibly bored as this is the last student this day, asks him a question.
-I will ask you only one, very simple, question. If your answer will be right you pass, if your answer will be wrong you fail. Do you agree?
Student, seeing his chance to avoid longer interrogation agrees.
-So, look, there's a glass of water standing at my desk, right? Also, there's beautiful weather outside, it's sunny and warm. Now touch the glass and tell me: why the side of the glass which is facing the window is colder than the other side. Don't hurry, take your time.
Student, a bit stunned, starts to answer after a long pause, but he visibly doesnt know the answer, because what he sees and feels is against laws of physics. But seeing his chance he starts to talk in an evasive manner, creating long sentences about sun rays, chemical characteristics of water, dispersion etc. hoping that professor will see that he's trying, even if he is telling bullshit. When he finishes, professor sighs and says:
-Unfortunately, my dear, you failed. I...
What did professor say to student?
