your weapon points at your mouse, the game is checking how fast your weapon is going, if its fast enough you will kill the enemies by swingings fast at them, which usualy means raising you mouse up and down FAST.
Ahhh. I didn't know that. I didn't see it written anywhere. I haven't played any games that do that kind of control scheme. Sorry.
understandable, I made it like that because it it gives a larger feeling of control.