The Virginia Opossum
The opossum's trick is so iconic that it's entered our vocabulary. We're told to "play possum" if a bear lumbers by, for example (incidentally, that's not always true: here's how to survive a bear attack). When predators get too close, opossums seize up and secrete a foul, corpse-y smell out of their butts. This defense mechanism is totally involuntary. You could pick up an opossum in this state and just walk away, because they don't "reanimate" until hours later. It's weird that such a high risk strategy could be so successful. Who knew that a coma and some farts was all it took to keep predators away?