Movie 2.

Animations of the simulated mandible show how the equal distribution of elastic energy produces the same dynamics in a mandible closure with and without a pin joint. When the energy is partitioned unequally, the mandible translates as well as rotates, disrupting the circular kinematics. If this unequal partition of energy is constrained to have a frictionless pin joint, then the compressive spring oscillates during mandible closure, decelerating the mandible.