Two point vortices alternate on/off (blinking). Each half-cycle: one vortex rotates all tracers around itself. The composition of two incompatible rotations generates chaos — KAM tori survive in regular islands, chaotic sea fills the rest.
2.0
0.60
1.5
800
Left: Tracer positions (colored by initial angle) | Right: Poincaré section (points at each switching moment)