Bubble Burst Challenge

Bubble Burst Challenge is a chain-reaction puzzle, not a bubble shooter: nothing is fired and nothing is matched by colour. The grid is solid with bubbles, and each one carries between zero and eight spikes on the eight compass directions. Tap a bubble to pop it, and a pulse leaves along every spike it had. Each pulse skips empty ground and stops at the first bubble still standing — which pops in turn, and sends out its own.