1. You start by describing a thing. 2. The next person draws a picture of it. 3. The next next person describes the picture. repeat steps 2 and 3 until everyone has either drawn or described the picture.
You then compare the first and last description... and look over the pictures. One of the best ever was:
Draw a penguin. The first picture was a penguin with a light shadow.
After going around five rounds, the final description was "a pidgeon stabbed with a fork in a pool of blood in Chicago"
I'm still trying to figure out how Chicago got in there.