To kill? A mockingbird.

Mockingbirds may look pretty much alike to people, but they can tell us apart and are quick to react to folks they don't like. Birds rapidly learn to identify people who have previously threatened their nests and sounded alarms and even attacked those folks, while ignoring others nearby, researchers report in Tuesday's edition of Proceedings of the National Academy of Sciences.

"This shows a bird is much more perceptive of its environment than people had previously suspected," said Douglas J. Levey, a professor in the zoology department of the University of Florida. (USA Today, 5/19/2009; hat tip to newsoftheweird.com)