You have to say one word then someone else has do say a word that has to do with it. For example: sea. Water. Squirtle. Pokemon. Japan.
This thread appeared in my "Suggested topics" at the bottom of another thread; I know that it's usually not popular to revive an old thread, but with the risk of getting unpopular, I'm adding my two pence:
spam --> MontyPython
Well if you're going to do monty python, then i must add parrot
Connecting to parrot, but still on Monty Python, I feel obligated to say swallow (European)