Venomous snakes are often perceived as aggressive antagonists, with the North American cottonmouth having a particularly notorious reputation for such villainy. We designed tests to measure the suite of behavioral responses by free-ranging cottonmouths to encounters with humans. When confronted, 23 (51%) of 45 tested tried to escape, and 28 (78%) of 36 tested used threat displays and other defensive tactics; only 13 of 36 cottonmouths bit an artificial hand used in the tests. Our findings challenge conventional wisdom about aggressive behavior in an animal perceived as more dangerous than it is. Changing irrational negative attitudes about venomous snakes is a necessary step toward quelling the recently documented global decline in reptiles.