Flip a coin—ears or tails?

Sci-fi is generally not my genre, and James Cameron is not a director I admire. But he said something interesting about why he gave tails to the creatures in Avatar: "Well, tails are cool. Tails are very expressive. I mean, anybody that owns a dog or a cat knows that you can tell the cat's emotional state by what its tail's doing." So I went to see the movie because I was entranced by the idea of humans with expressive tails. The idea made my behind wiggle in anticipation.

But in the end, the tail thing was kind of meh. And it was the length of the movie, not the tails, that kept my behind wiggling. But the ears! They moved! And it made me wish for ears that tracked sound—and made me wonder why I don't have them. Every other mammal I can think of has ears that rotate, cock, flop and twitch. Why not me? I just know my hearing problem would go away if I had my rightful mammal ears.