If you thought Fifty Shades of Grey got a bit rough, wait until you see fifty shades of grey reef shark. 

Catching sharks in the act is always an unforgettable experience, even for seasoned underwater photographers like Yann Hubert. Along with rays, they have some of the most diverse reproduction methods of any animal group. Some lay eggs, some give live birth and some even manage the feat without a partner. For many other shark species, an offshore lifestyle means experts are still discovering the ins and outs (no pun intended). 

While it looks extremely intense, the biting behaviour in this video is necessary to ensure the mating pair sticks together. Scientists have observed that female sharks tend to have thicker skin than males – and after watching the clip, it's easy to see why that might come in handy. Our best guess is that thick skin keeps the body cavity from being penetrated during, well, penetration. 

By latching on to the female's fin, the male remains close enough for one of his two – yes two – reproductive organs (known as claspers) to deliver his contribution.  

And why the two "penises"? Unlike a true penis, a shark's claspers aren't an independent appendage. They're actually extensions of the pelvic fins (the paired fins located on the shark's underside). Grooves within the claspers help channel semen where it needs to go. There are two of them simply because there are two pelvic fins to begin with. 

Interestingly, research suggests that sharks use only one clasper at a time – the side opposite the "docking" side is used more often. A pair of tope sharks (Galeorhinus galeus) were reportedly found locked belly to belly by both of the male's claspers, but as far as we know, that's not a go-to manoeuvre. 

To ensure its place within the female is secure, the clasper's tip unfolds once inserted, sometimes anchoring with spike-like "clasper spurs". 

It all sounds quite painful, but don't call Neil deGrasse Tyson just yet. Shark biologist Dr Neil Hammerschlag explains that the sensory receptors (known as nociceptors) responsible for feeling pain in humans and other mammals are not present in the sharks studied to date. This suggests the animals' response to injury is more of a reflex than a reaction to "pain" as we know it. 

All that said, shark sex is not even close to as weird as it gets in the ocean. Just look at the detatchable, free-swimming "penis" of the paper nautilus.

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Top header image: Robin Hughes/Flickr