Thanks a lot Michał. I appreciate the kind words.
The head/leg collision is line-line, using multiple lines for the skull, similar to line-rect collision detection http://jeffreythompson.org/collision-detection/line-rect.php
The bounce is... uh... more complicated and involved a heck of a lot of testing and tweaking before it felt comfortable. Hit me up anytime you want to hear more about the gory details :D