For my recent gm48 entry I made some trees with physics-like attributes using procedural generation and recursion. The player controls a chameleon (which uses circle intersections for IK joints and it figures out where to place the feet). The chameleon follows the mouse cursor and can move between trees and branches. The theme for the gm48 was "color is important" so my implementation was to make the flies essentially fly away from the player if they're not matching the leaf color (using the mouse wheel to control hue) otherwise they're easy pickings.
If you're having trouble understanding some of the code let me know (this was made in 48 hours so it's not heavily documented). I'm more easily reached through twitter: https://twitter.com/voxeledphoton
Thank you for the interest and/or support, have fun! ;D