As any armchair ichthyologist will tell you, the most sensitive part of a shark is its electroreceptive snout. This has given rise to the belief that a sharp punch in the nose will repel almost any shark attack. As it turns out, this is usually a very bad idea that can result in losing your fingers, hand or even arm. Here's what you should do instead.
IFLScience recently debunked 10 homespun survival myths that the Bear Grylls wannabes of the world loudly swear by. In reality, most of these "survival tips" will put you in a worse predicament than before and could even kill you outright.
This includes the widely held belief that punching a shark on the nose will convince it to bugger off and bother some mackerel or something. While it's true that sharks don't enjoy having their noses messed with, the chances of landing a solid punch underwater are perilously slim. You're a lot more likely to badly gash your knuckles on its teeth and trigger a feeding frenzy.
Even if your aim is true, the success of the counterattack will largely depend on how committed the shark is to eating prey at that particular moment. If the shark is old or starving (which maneaters often are), a whack on the nose with your comically ineffectual hands is unlikely to put it off its dinner.
According to the brain boffins at IFLScience, you should try searching for a large solid object instead:
It’s really hard to land a solid punch on the nose of a moving shark. In the rare cases where a shark comes in for a bite, try to put a solid object between you and animal. If that fails, claw at its eyes and gills.
So the next time you're chilling in the ocean and a distressingly large dorsal fin makes a beeline towards you, save the schnoz chop-socky as an absolute last resort. You can find more information on shark repellents and survival tips here and here.