I used to love these lateral thinking puzzles as a teenager.  I got burned on one, once: I'll reproduce the situation and some of the questions here, and post the answer below some spoiler space.  The rules were that a question could be answered yes, no, or maybe; "maybe" was supposed to be used only if there was an ambiguity in the question that the questioner presumably wasn't aware of.  The dialog below is more or less the questions I asked, many years ago.

Situation: there is a a plane over the sea.

Is there anyone in the plane?  Yes.
Is there a pilot?  No.
Is the plane crashing?  No.
Are there any passengers?  No.
But there is someone in the plane? Yes.
Is it a stowaway? Maybe.
Did they have a ticket? No.
Did they get on the plane without anyone seeing them?  No.
Is it a case of mistaken identity?  Maybe.
Is the plane over the North Sea? Yes.
Is it going to Britain? No.
To Scandinavia? Yes.
To Finland? No.
To Denmark? No.
To Sweden? No.
To Norway? Maybe.
To Oslo? Yes.
So it's only maybe going to Norway, but it's definitely going to Oslo? Yes.
Is the stowaway from Norway? Maybe.
Is it a man? No.
Is it a woman? No.
A child? No.
A hermaphrodite? Yes.
So we have a hermaphrodite stowaway in a plane over the North Sea, going to Oslo? Yes.
Is the hermaphrodite alone?  Yes.
Alive?  Yes.
Are there any dead bodies on the plane?  Yes.
More than a hundred? No.
More than ten? No.
More than five? Yes.
Nine? Yes.
Were any of them passengers? No.
Crew? No.
Acquaintances of the hermaphrodite? Yes.
Did he/she kill them? No.
Was he/she involved in their deaths in any way? Maybe.
Did they die on the plane?  Yes.
Was it an accident?  No.
Was it murder? No.
Death by natural causes?  No.
Disease?  Yes.
Did all of them die of a disease?  Yes.
The same disease?  Yes.
Does the hermaphrodite have the disease?  Yes.
Is he/she going to die of it too?  Yes.
Before they reach Norway?  Maybe.


OK, that's about as far as I got before I decided I didn't have a clue what was going on and asked for the solution.  The answer is below after some spoiler space.






























The setup is a trick; or you could say it requires far more lateral thinking than any of the other puzzles.  If the question ends with a vowel, the answer is yes.  If it ends with a consonant, the answer is no.  If it ends in "y", the answer is "maybe".

My girlfriend's father pulled this on me back in 1978.  I was so sure I could solve any lateral thinking puzzle; he fixed me good.

In practice, if you want to inflict this on someone else, you should make a big deal of thinking about some of the answers, and saying things like "Well, the way you asked the question, the answer has to be 'yes'", and so on. 

Mike Christie