A lot of people are afraid of snakes and the fear makes total sense, even if most snake bites aren't lethal. As it turns out, they can actually send you back in time. At least, the Russell's pit viper's bite can give you symptoms that mimic the loss of puberty. From io9:

"What distinguishes [Russell's Viper victims] is a sort of reverse-puberty in adults. They lose their sex drive. They lose fertility. They lose their body hair, especially pubic hair. Men lose facial hair and muscles. Women lose curves as the condition causes them to lose weight. Some doctors even report loss of mental faculties as the condition progresses."

Indiana Jones' fear of snakes suddenly seems a lot more rational.

[Image courtesy of Mark Mannetti of Wikipedia]