It seems that I wasn’t the only person to get in for free to a screening of Snakes on a Plane; someone in Arizona thought it would be funny to release two venomous rattlesnakes during the film. Bring on the experts:
“That to me is very scary,” herpetological association representative Tom Whiting said. “I would hate to be watching a movie about snakes and have a rattlesnake bite me.”
Presumably it wouldn’t be scary at all to be bitten by a rattlesnake during, say, Titanic.

When I heard this, I came up with a list of movies that could never pull that off:
Cars
Pirates of the Caribbean
Bats
Night of the Living Dead