The practice may not be the result of pure thuggery, however. Sports psychologist Paul Penna, who has assisted with NRL teams and the A-League, said biting can be an automatic response to circumstances on the field.

''When you're exuding that much energy your mouth is open already,'' he said. ''It makes it really easy to shove something in there and the natural impact is to clamp down on it.''

Biting is more likely to be an inappropriate instinct than a psychological tactic or reaction, psychologists said. But it could also be prompted by aggressive coaching strategies designed to rattle the other team.

''There's a line in every sport, and some athletes can comfortably go up to it and feel in control. But there's a line that some athletes go up to and lose their control," Mr Penna said.

Kirsten Peterson, head of psychology at the Australian Institute of Sport, said she had not encountered incidents of female athletes biting, and this was characteristic of our different biological responses to threat. Women facing danger are more likely to withdraw or get depressed rather than fight back, she said.

Psychologists were surprised that Suarez, a talented and accomplished athlete playing at the sport's highest level, would undermine himself by biting an opponent. But in a match of such intensity "something just hits automatic pilot", Mr Penna said.

But Boxer Mike Tyson, sport's most famous biter after he chewed off half an ear in 1997, is in a rather different league. Having marched over to Evander Holyfield seething with intent, he was "just an animal that was enraged''.