[kombucha]

This is the same question I had in my last thread, but I was told to have one concept per thread.
So how does Flash collision detection work? There is no way all games use bounding-box collision detection. For example, if I want to know when a ball is hitting a line at 45 degrees, how do I tell when it hits anything but the highest point accurately? Or if I have a person, how do I know if a nail hits anything but its outstretched arm accurately? Two movie clips must have some way of calculating opaqueness when colliding.... right?
Remember, I'm a n00b... I don't know what classes are