Some sharks can be placed in a tonic state when flipped over. The shark remains in this state of paralysis for an average of fifteen minutes before it recovers.
Scientists believe that tonic immobility, displayed by sharks, may be linked with defence, because female sharks seem more responsive than others. During tonic immobility, the dorsal fins straighten, and both breathing and muscle contractions become more steady and relaxed.
In some cases though, tonic immobility may prove a real danger for sharks. In the first recorded eye witness case of predation on a great white shark in the wild by a species (other than humans) a female orca (also known as the killer whale) was seen purposely inducing tonic immobility in a great white shark by tipping the shark upside down; this kept the shark still for fifteen minutes, causing it to suffocate and die.