When California ground squirrels (Spermophilus beecheyi) are confronted by snakes, they puff up their tails and wave them around, in a display called tail flagging. Snakes are sometimes deterred by this behavior. Aaron Rundus, a biologist at the University of Nebraska-Lincoln, and his colleagues watched squirrels under an infrared camera. They discovered that in response to some snakes, squirrels aren't just wagging their tails, they are heating them too. The study is published in the August 17, 2007 online issue of the Proceedings of the National Academy of Science.