If you are an experimentalist, please just skip it. I'll post something for you tomorrow.
Here is a famous test by Karl Duncker, he created it to study the "functional fixedness". So, you have a candle, a box of thumb-tacks and a book of matches:
The task is to attach the candle to the wall, in such a way that the wax doesn't drip onto the table (or the wall).
This is not kind of complicated, or is it? However the results of Duncker's studies were amazing - people solving the problem just to make fun were much faster than those, who were promised a reward (say, 50 dollars) for being the fastest.