Mating Antelope Show Off Knees. Seriously.

Doesn't sound all that sexy, but Africa’s male eland antelope has developed his own way of demonstrating its sexual prowess and warding off rivals. Males click their knees to establish mating rights and avoid brawls: the louder the click, the larger the animal, and the more likely he is to defeat a challenger. Like "a string being plucked," the sound travels hundreds of meters, researchers tell the BBC.
(More antelope stories.)