What is Tonic immobility?
[[File:BatrixNatrixBellyPattern.JPG|right|thumb|A [[grass snake]] upsidedown, playing dead]] '''Tonic immobility''' is a natural state of [[paralysis]] that animals enter, often called '''animal hypnosis'''. Its function is not certain. It may be related to mating in certain animals like [[Shark|sharks]] and [[mammal]]s. It may also be a way of [[Anti-predator defences|avoiding or deterring predators]] (playing dead is called '''thanatosis'''). The term '''tonic immobility''' has also been used for the [[paralysis]] that often immobilizes animals, such as rodents or birds, when they feel threatened by a [[predator]]. Tonic immobility plays a role in survival if it helps a hunted animal to blend in with its surroundings. Tonic immobility can be induced without causing any apparent stress to the animal. For example, stroking a particular area of a [[lobster]]'s shell or focusing a [[hen]]'s attention on a line on the ground. {{fact|date=July 2024}} Tonic immobility has also been said to occur in humans that are subject to intense trauma, such as [[rape]] or sexual assault.{{Citation needed|date=March 2024}}[[Catatonia]] in humans is a serious [[psychiatric]] condition that often involves a state of immobility. == Sharks == Some sharks can be placed in a [[catatonia|tonic]] state.<ref name=Hen>Henningsen A.D. 1994. Tonic immobility in 12 elasmobranchs: use as an aid in captive husbandry. ''Zoo Biology'' '''13''': 325-332 {{doi|10.1002/zoo.1430130406}}</ref> The shark remains in this state of paralysis for an average of fifteen [[minute]]s before it recovers. Scientists have exploited this [[phenomenon]] to study shark behaviour. Some sharks go into tonic immobility when they are turned upside down. With [[tiger shark]]s (measuring 3–4 metres, or 10–15 feet, in length), tonic immobility may be achieved by placing hands lightly on the sides of the animal's snout in the area surrounding its eyes. Scientists believe that tonic immobility in sharks may be related to mating, because female sharks seem more resp