Centuries of evolution have made the lion a patient predator. In this video, a lion hides among the rocks and sand surrounding a watering hole, all the while studying the unsuspecting impalas and waiting for the right moment to strike. If all goes well — the impalas aren't spooked and the lion's hunting companion is ready — there will be impala for lunch.
Of course, checking the depth of the watering hole might also be a good pre-ambush planning strategy, too. (It helps avoid cannonball-sized splashes and other embarrassing hunting fails.)