ABSTRACT
Tonic immobility is the final defence in a chain of anti-predator responses involved in maintaining survival (Ramos et al. 1999). It involves a temporary profound state of motor inhibition. It may be activated by proximity to the threat, restraint or other physical contact between predator and prey, in situations appearing hopeless. In some species, such as sharks, turning the animal upside down may induce it. Turning these vertebrates upside down also results in their becoming long-sighted in trance-like states (Hueter et al. 2001). This is very different from attentive immobility associated with highly vigilant risk assessment, with options including flight and counterattack. These two forms of immobility are different evolutionary phenomena masquerading under an illusion of similarity.
