An invisible rabbit sits on one of the posts of an infinite fence. A local farmer cannot stand this fact and wants to shoot the rabbit down*. Every time the farmer shoots her gun, the rabbit jumps to another post along the fence (not quickly enough to avoid the shot, though). The jump is always in the same direction and the same distance.
How can the farmer make sure she hits the rabbit with a finite number of shots?
* Not to kill it, of course, just to get it off the fence. It's a water gun.