Tonic immobility is a natural state of paralysis which animals enter, often called animal hypnosis. Its function is not certain. It may be related to mating in certain animals like sharks. It may also be a way of avoiding or deterring predators (playing dead is called thanatosis). It is also a temporary state of motor inhibition believed to be a response to situations involving extreme fear. In humans, Tonic Immobility is believed to occur during times of disaster and turmoil.