Tap two identical hunks. They clear if you can join them with a line that runs through empty space and turns no more than twice - they don't have to be next to each other, and the line can travel around the outside of the board, which is how you get going while it's still full. A pair that can't be joined flashes red. Every tile you clear opens up space for the next move, so work the edges first. Sit still for a few seconds and a playable pair lights up on its own, and if no move is left at all the board reshuffles itself.
