While these snakes don't always have the most deadly bites, they have the most painful ones.
Van Wallach of the Harvard Museum of Comparative Zoology has had several viper bites; the worst one, he said, "came from an African bush viper. It felt like somebody had a blowtorch and was burning you inside your arm. … It went on for three straight days before I had any relief."
Kelly Zamudio, a biologist at Cornell University, described a similar sensation when she was bitten by another member of the viper family — the rattlesnake.
"It feels like burning, like you're being branded, but the brand never lifts," she said.
The key to the excruciating pain of the viper's bite is its tissue-destroying venom, which dissolves cell walls and causes internal bleeding. As the venom works its way through the body, so does the pain.
Vipers' tissue-eating venom isn't designed to hurt humans, but rather, to get a jump on digesting their food. When the snake strikes a rodent, bird or another type of prey, the toxins work quickly to help breaking down the tissue and get the meal ready for eating.
Although these animals gained a bad rep after the tragic Steve Irwin incident, stingrays are not aggressive or (usually) lethal animals. However, they have a sting, and on the rare occasion they choose to use it, "it's very excruciating," said Edward DeMartini, a research biologist at the National Oceanic and Atmospheric Administration fisheries.
When these gentle animals are stepped on or threatened, they will strike out with a sharp, serrated barb — about the thickness of a golf pencil — located at the base of the tail.
"The physical wound can be pretty intense," said Jon Hoech, director of husbandry operations at the Monterey Bay Aquarium. "It's extremely painful, like getting punctured with an eight-penny nail. Also, it's like a cat scratch, it can carry a lot of bacteria."
On top of the sizeable puncture wound comes a dose of toxins that cause instantaneous pain.
Stingrays only use their venomous barbs as a defense, not for hunting or attacking. As many marine biologists, scuba divers and snorkelers know, the animals are the ocean's pussycats.
"I work with rays on a regular basis," said Hoech. "I swim with them, I feed them by hand, and they're very benign." Just be sure to look where you step.
There are thousands of scorpion species, all of them equipped with stings. Many species' stings aren't much worse than a bee or hornet; but a select few can be a serious source of suffering.
"There are scorpions in the Old World that have extremely painful stings," said Don Boyer. "It gets worse and worse and worse."
These types of scorpions — found in Africa and Asia — can be dangerous as well as painful. However, in the Southwestern United States, the Arizona Bark Scorpion doesn't pose much of a threat to healthy adults. It just means extreme pain.
"If you're an adult and you get the poison in your finger, it just stays, and fires your pain nerve," said Dr. Leslie Boyer — no relation to Don Boyer. "It locks the nerve in the on position."
Leslie Boyer, who is medical director of the Arizona Poison and Drug Information Center, said that the tiny sting will "send shooting sensations up your arm." If you're clumsy enough to tap or bump that finger on anything, the pain instantly amplifies.