small niggle. what is a verlet constraint? (rhetorical)

whilst its obvious that you have just discovered verlet integration and the relaxation method of applying constraints - because everyone goes off and writes a physics engine at this point - i only think i know what you mean because i have assumed this.

are these length constraints, angle constraints etc?

still... no matter how common and unexciting this is for me, its always cool to play with physics simulations for five minutes. thanks for sharing. :)