Try to clear groups of identical animal head icons by swapping one icon with an adjacent to form horizontal or vertical lines of 3 or more identical icons. The group is cleared and the icons above fall down (and new ones enter the field from the top) sometimes creating chain reactions. The more icons you clear, the more points.
As you progress, the variety of icon types will increase, making it harder and harder to find valid groups. A timer makes sure you can't relax for long, game over when time over.