This movie shows accelerating waves in a BZ-AOT microemulsion. Just below and to the left of the center of the picture, waves collide. Note how they speed up just before collision and then appear to bounce off at right angles after the collision. In ordinary aqueous media, BZ waves travel at constant velocity and disappear when the collide with each other rather than bouncing off. For more details, see:

V. K. Vanag and I. R. Epstein, "Pattern Formation in a Tunable Reaction-Diffusion Medium: The BZ Reaction in an Aerosol OT Microemulsion," Phys. Rev. Lett. 87, 228301-1-4 (2001).