whats this trick

hey whats this trickis it hard and is anyone able to give me advice on it.
i think its called a seat drop well that would make sense.

heres what it is http://www.youtube.com/watch?v=YPChBSaV8o0

That is a seat bounce

yeah and its not fair cause some seats just dont work. I never understood the trick tried it on matt’s uni and it worked first time. Damnit.