Tonic immobility
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.