I love the various little games that keep getting thrown up in semi-scientific contexts that show how complex (and at the same time simple) our minds really are, here is an example I enjoyed:
I'm thinking of three words: one means "a mythical being", the second is "the name of a building material", and the third is "a unit of time", What words do I have in mind?
It's not difficult to think of three words that fit the descriptions, but it is unlikely you’ll pick the three I had in mind. Now try a second task:
This time I'm looking for rhyming words. I'm thinking of three words: one rhymes with "post", the second with "eel" and the third with "ear". What words am I thinking of?
Again, you can think of three words which match the descriptions easily, but which ones did I have in mind, last but not least:
Suppose I tell you the words I seek are the same in both tasks: What is a word that means a mythical being and rhymes with "post"? What word is the name of a building material and rhymes with "eel"? And what word is a unit of time and rhymes with "ear"?
Now the task is easy, the combination of just two constraints reduces the selection until there are only three words which fit… "ghost", "steel" and "year"!
This was taken from a book I'm rather enjoying called "The Design of Everyday Things" by Donald A. Norman which is a bit of an engineers book to be honest, but is good bed time reading all the same (or whisky supping reading at least!)
(and no this isn't one of those horrible pay per post things, if you want to read it try a library :P )