This is neat and something I didn't know until just now:
"Ear flaps of owls are very different - one ear flap is higher than the other, and the ear openings are shaped differently. Any given sound is different in each ear, so the owl can "focus" the sound by moving its head until the sound is the same in both ears. Then the thing making the sound is right in front of the owl.
Any owl's sense of hearing is much better than a human's. The facial discs (the ring of special feathers around each side of the face) appear to be around the eyes, but are actually around the ears which are right behind the eyes. Each ear is a different shape from the other and in a different position on the skull. That, coupled with the "fence" of feathers down the center of the face over the beak, makes sound reception different in each ear, and the owl can skillfully focus the sound and pin-point its location exactly. Flying at the sound with feet outstretched in front of its face allows the owl to strike its target even in total darkness."