Hypnotised Shark

Tonic immobility as a scientific tool
According to Gilman et al. the investigation of ‘animal hypnosis’ dates back to the year 1646 in a report by Kircher. As a scientific tool, tonic immobility is considered to be a fear-potentiated response induced by physical restraint and characterised by reduced responsiveness to external stimulation. It has been used as a measure in the assessment of animal welfare, particularly hens, since 1970. The rationale for the tonic immobility test is that the experimenter simulates a predator thereby eliciting an anti-predator response - "death feigning". The precept is that the prey animal 'pretends' to be dead to be able to escape when/if the predator relaxes its concentration. Death feigning birds often take advantage of escape opportunities; tonic immobility in quail reduces the probability of the birds being predated by cats.
To induce tonic immobility, the animal is gently restrained on its side or back for a period of time, e.g. 15 seconds. This is done either on a firm, flat surface or sometimes in a purpose-built ‘V’ or ‘U’-shaped restraining cradle. In rodents, the response is sometimes induced by additionally pinching or attaching a clamp to the skin at the nape of the neck. Scientists record behaviours such as the number of inductions (15 second restraining periods) required for the animal to remain still, the latency to the first major movements (often cycling motions of the legs), latency to first head or eye movements and the duration of immobility, sometimes called the ‘righting time’.