The bamboo pit viper of Vietnam is chock full of hemotoxic venom, which works by disrupting the blood's clotting process, destroying red blood cells, and wreaking havoc on your organ tissues. They were known as three-step snakes, because that's as far as you'd make it after getting bit by one. Now, it's bad enough to be burdened with the knowledge of such a creature, much less to have even the remotest possibility of stepping on something like that in the dense underbrush. But during the Vietnam War, the Viet Cong made everything worse when they started using them as natural biological weapons.
They hid pit vipers in their packs so that anyone searching through them would get an agonizingly fatal surprise. In the tunnel complexes, they stuffed them into pieces of hollow bamboo and propped them in places where U.S. "tunnel rats" were likely to stick their unwary hands. Worst of all, they tied them into the branches of trees by their tails, right at face height. After a couple days spent hanging in a tree without food, the snake would be (admittedly, justifiably) pissed. And at that point, it would lash out at anything that came within range, even your goddamn eyeball. Especially your goddamn eyeball.
"Don't worry. I'll settle for other balls, too."