It goes like this. One person says 'give me...' and they name something. Then another person goes and finds a picture of that something and put it here. Then they say 'Give me...' and so on and so forth.
Example
Person 1: Give me a cow.
Person 2:

Give me ....
You get it?
Okay, the official start.
Gimme a monkey!
Edit: Before this happens (because I'm afraid it will) don't request porn. EVER. Doing so will cause me to smite you. Making a joke (like the smexking pigeons) is fine, but don't ask for a hot blonde or something that could cause a lot of trouble. Kay? Kay!