The Swell Shark

  The swell shark is a thoroughly interesting species of shark. It dwells in crevices in tropical reefs by day and merges to hunt come nightfall. They are small sharks that are generally shy around divers. As they grow only to an estimated one hundred centimetres long, they have reason to hide away for fear of discovery by larger reef sharks which may have an intent to kill it.
  The diet of a swell shark consists of small fish and crustaceans. Amazingly, these opportunistic creatures have been known to enter lobster pots to find an easy meal. In turn, these sharks are the prey of many other marine specimens. However, swell sharks do have a stunning defensive technique: as it says in their name, a swell shark will jam itself between two rocks and inhale water to make itself impossible to extract from its position. When the predator has left the vicinity, the shark exhales and swims away. Simple, yet remarkable.
  Swell sharks are found on reefs in the East Pacific, along the West coast of North and South America and throughout the tropical waters of Hawaii. Although they are not generally dangerous to humans, they have been known to act threateningly and even aggressively if a diver comes to near or appears to be a predator. They have also occasionally been known to bite a diver's limb as a warning, but with no fatalities.

A swell shark off the shore of Western North America.

A swell shark jammed between two rocks in defence.