Why does a clothes peg fly forward when released?

[Pandemonium]

When we press down a clothes peg (those big, plastic ones), and then let our fingers slip off it, the clothes peg will snap close and fly forward. Which force and its components are responsible for this forward motion?

 

[selfAdjoint]

Because of the shape and slipperiness of the pegs, it is practically impossible to press down with a force truly at right angles to the peg's axis. So the pressing force, and its reaction force (Newton's third) upward from the surface the peg is lying on have both got components in the forward direction. And the vector sum of those two forces has a double component in that direction. It is this forward force that shoots the peg out.

This same demo used to be done with cherry pits in the old days.