It is most people's worst nightmare, but one bloke has set about spending his life getting bitten more than one thousand times by sharks.
Why? In the name of science, of course.
Jeremiah Sullivan is a marine biologist out of San Diego is one of the world's leading experts on the interaction between humans and sharks.
He's put the hours into being as well respected as he is, too. Since the early 1970s he's been studying how we get along with some of the ocean's most fearsome creatures.
Jeremiah, who is into his 60s these days, spends his time getting chewed and chomped on by animals that most people wouldn't even get into the water with.
Jeremiah Sullivan. Credit: Facebook
It's tough work, but someone has got to do it if we're to understand better how to test shark behaviour and to ensure that humans and sharks can co-exist in a peaceful - or at least safer - way.
Jeremiah also makes special suits that are aimed at helping humans survive getting bitten by sharks.
How do you test those suits? You've guessed it - Jeremiah has to get bitten, again.
Don't worry though, he loves it.
He told the Daily Beast: "I've been bitten thousands of times.
"Been thrown around a bit. Beaten up pretty good. Nearly had my teeth knocked out. Certainly chewed on a lot."
Don't try this at home. Not least because the shark will die. Credit: National Geographic/Man vs Shark
If this interests you, you can watch Jeremiah in action on National Geographic's show Man vs Shark.
In one episode, he takes a few nibbles from a 14-foot tiger shark, with the aim of testing his newest suit which - if he is to be believed - could withstand an axe blow.
Tiger sharks can bite with up to 400lbs of force and have a nasty habit of chewing up and ripping through pretty much anything they take a fancy to.
However, up against Jeremiah's special suit they really struggle. Superficial damage at best.
He continued: "I felt pretty confident in what I was doing but the tiger sharks I'd been saving for later, they're known to have among the most destructive bites and to do a lot of damage when they get a hold of things and try to chew on them for a bit.
"We weren't sure what was going to happen. I had a lot of people with me that were quite sure that when one bit me, the other tiger sharks were gonna come swarm on me."
Jeremy has built up something of a rapport with sharks over the years, he's hitched a ride on great whites and rejected advances from hammerheads, but that doesn't mean that he's not still a bit shaky before he goes into these places.
Look at those teeth. Credit: National Geographic/Man vs Shark
He added: "I'm not fearless at all.
"Fear is a funny thing. Fear of the unknown is really all it comes down to, so if you're well-informed about the environments you're going into, and prepared as can be, it puts you in a pretty good position.
"Being a water guy and in the ocean virtually my whole life, it's not something that's frightening or fearful to me. It's more like home."
Featured Image Credit: National Geographic/Man vs Shark