What makes a stone bounce repeatedly when thrown across the surface of a lake, and how many bounces can it perform?
This fascinating piece describes much of the physics at work, thanks partly to special equipment that simulates the skipping and records motions.
The short answer: A combination of rotational velocity, the stone's shape and physical throwing speed enables hurlers to maximize the number of skips. The article goes into far greater detail about the mathematics behind skipping stones.
A nice bonus you'll get a kick out of, as I did, is a free link to a video of the longest stone skipping ever recorded. It earned the hurler a place in the Guinness Book of World Records.