So let's say you're a common ground squirrel. Just for a moment, pretend you're minding your own business, searching for seeds, doing whatever it is that squirrels like to do. Then, suddenly, out from behind a bush slithers a huge, sinister rattlesnake, coiled and ready to strike. What do you do?
Obviously, you run away, play dead, or perhaps negotiate a deal of some sort. In any case, given that you're a furry, gentle squirrel and the snake is a deadly, rattling killer, whatever you do, you don't stand your ground and fight. Right?
Wrong! Calling upon the instincts passed down from your ancient squirrel ancestors, you rush at the snake, kick sand in its face, try to bite its tail, and then turn your back on it and whip your tail around.
Now why on earth, you might be wondering, would my squirrel self take such suicidal measures? Kicking sand and biting might do some good, but tail waving? Why further taunt a venom-fanged snake already bent on violence?
As you may have guessed, there is a method to such madness. When confronted by a rattlesnake, squirrels' tails heat up, getting hotter by almost four degrees Fahrenheit. The infra-red sensors built into rattlesnakes' eye sockets sense this increase in temperature as a big, waving, fiery blotch.
This alarming display, plus the fact that squirrels are partially immune to rattlesnake venom, actually gives the squirrel a distinct advantage when it confronts a rattlesnake. More often than not, the rattlesnake will slither away in search of a less intimidating foe.