A pair of snorkellers found themselves tangled up in an eight-arm brawl recently after they got a bit too close to a hungry moray eel and its octopus prey.

The clip was filmed off Hawaii's Oahu coast by tourists Nicklas and Elin, who were visiting the islands from Sweden.

"Some think it's cool, others think it's stupid. Do not get too close to a moray eel and its prey is what we learned that morning!" they wrote on YouTube. And that rule of thumb doesn't just apply to feasting eels. Last year, Earth Touch cameraman Bart Lukasik had a similar encounter when he entered a moray's cave abode.

To be clear, the large eels are not always aggressive, and typically won't attack a diver. The problem arises when the animals feel threatened – and as interlopers in their marine habitat, it's up to us to ensure that situation doesn't arise. In fact, one of the worst eel bites we've seen occurred after a dive master attempted to touch and feed a moray.

Eel teeth aren't exceptionally large (most are less than one inch, or 2.5cm, in length) – but it's not size that matters here. The teeth are recurved, which means they point toward the back of the mouth, and that makes escaping an eel's clamped jaws particularly difficult. It's a phenomenon known as the "pull-back effect": your instincts tell you to pull back your trapped limb, but in doing so, you unintentionally drive the eel's teeth deeper into your flesh. 

And if one set of jaws doesn't scare you off, you should know that these eels have a second set, the pharyngeal jaws. Located in the back of the throat, the pharyngeal jaws act as backup to tear prey (or an unsuspecting arm) into bite-sized morsels. They also add to an eel's grip force, as they can be thrust forward once the first set of jaws has latched on. 

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A moray eel has two sets of jaws. Image: National Science Foundation/Wikimedia Commons

As for the Hawaii eel's tentacled target, the octopus did manage to escape – and that mostly down to luck. Clinging on to an attacking eel is an acceptable defence strategy, but you'll notice that the eel reacted to the crafty cephalopod's tactic by twisting its body into a coil. That motion, which ripped several of the octopus's arms from its body, can generate enough force to break bone!
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Top header image: Simen S/Flickr