So, this is how it works - someone says they go back in time and do something, then you say how it creates a paradox.
Example:
Poster 1: I go back in time and eat a candy bar.
Poster 2: That candy bar was the last on the shelf and meant for a starving man, so he dies, and it creates a TIME PARADOX!!
I go back in time a kill a baby.
Poster 3: That baby was Albert Einstein. You just created a TIME PARADOX!!
etc.
So, all be first.
I go back in time and eat a salad.

