Stirring fluid with a `taffy pulling' device

The four-pronged taffy pulling machine is a classic candy-making device. Two intersecting U-shaped pieces stretch and fold the taffy as they rotate. We demonstrate that this mechanism is an effective tool for stirring viscous fluid. The rods `braid' the fluid in a way that guarantees exponential stretching of non-trivial material lines. We analyze this stirring experimentally and using methods from topology and dynamical systems theory.