Tiny trap-jaw ant (Odontomachus brunneus) mandibles close within an average of 77 µs, with angular velocities on the order of 104 rad/s (470,000 rpm). Based on a new empirical dataset of 99 strikes from 10 individual ants, we discover that the mandibles close in a circular arc as if constrained by a mechanical pin joint. However, trap-jaw mandibles lack such a mechanical pin joint. Kinematic models of elastic loading prior to strikes reveal that elastic energy is distributed and delivered equally between the muscle-apodeme unit and head capsule. Dynamic models show how this equal distribution of elastic energy storage results in a circular trajectory, with or without a mathematical pin joint constraint. Furthermore, deviations from equal energy allocation between the springs results in a net translation and disruption of the mandible’s circular trajectory. Therefore, the circular trajectory of the mandible tips is a result of dual and equal elastic energy allocation between the muscle-apodeme unit and head capsule: the applied forces from their respective recoil accelerate the mandible in a circular trajectory with a fixed center of rotation yet without the constraints of a physical pin joint. These dynamics are analogous to “devil sticks” – juggling sticks that spin around a pivot defined by the applied forces of the juggler rather than by a joint constraint. The elegance and simplicity of using a partition of elastic energy to eliminate the need for kinematic constraints lead us to conclude that these devilish dynamics may be used by many spring-actuated biological systems.