Tonic immobility is a natural state of paralysis that animals enter, in most cases when presented with a threat.
Some sharks can be placed in a tonic immobility state by turning them upside down. The shark remains in this state of paralysis for an average of fifteen minutes before it recovers. Scientists have exploited this phenomenon to study shark behaviour.Usually when being testing sharks under this "tonic" state, scientists will put a chemical plume in the water awakening the shark.
Sharks may not always respond to tonic immobility by physical inversion of the animal as has been done with lemon and reef sharks. With tiger sharks 10 to 15 feet in length, tonic immobility may be achieved by placing hands lightly on the sides of the animal's snout approximately to the general area surrounding its eyes. Great white sharks have been shown to be not as responsive as other species whenever tonic immobility has been attempted. Scientists believe that tonic, displayed by sharks, may be linked with defense because female sharks seem more responsive than others During tonic immobility, the dorsal fin straighten and both breathing and muscle contraction becomes more steady and relaxed.
Tonic immobility also can be somewhat effective on anole lizards and a loose study was done with tonic immobility with the rabbit. Both were inconsistent examples of tonic immobility.
Tonic immobility has also been used to describe the paralysis which often immobilizes animals such as rodents or birds when they feel threatened by a predator. It can be argued that tonic immobility plays a role in survival if it helps a hunted animal to blend in with its surroundings by remaining as motionless as an inanimate object. This tonic state is common with invertebrates as well.Inducing tonic immobility in common animals requires, in some cases, extreme treatment such as electric shock along with other elements that produce stress.Contrary to popular belief, theories regarding "putting a lobster to sleep" seem to be rumors without empirical data to confirm their validity
