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When threatened, iguanas, monitors and other lizards tend to display defensive aggression. They stand sideways to the threat, swallow air to increase their size, stand high off the ground to look bigger and lash at the threat with their tails. Some lizards may display head bobbing and push-ups or gape and threaten to bite.

When threatened, iguanas, monitors and other lizards tend to display defensive aggression. They stand sideways to the threat, swallow air to increase their size, stand high off the ground to look bigger and lash at the threat with their tails. Some lizards may display head bobbing and push-ups or gape and threaten to bite.

* When threatened or molested by other animals, such as dogs, coyotes or foxes, certain horned lizards (''Phrynosoma cornutum, P. coronatum and P. solare'') will respond by squirting a spectacular amount of blood from their eyes. They accomplish this by constricting venous outflow from the head which increases blood pressure and causes leakage from the ocular venous sinuses.

* When threatened or molested by other animals, such as dogs, coyotes or foxes, certain horned lizards (''Phrynosoma cornutum, P. coronatum and P. solare'') will respond by squirting a spectacular amount of blood from their eyes.  

Defensive behaviour is associated with territoriality, escape from potential predators or may be ritualised with reproduction or feeding. It may be exhibited with humans, conspecifics, other animals or with no stimulation.

Defensive behaviour is associated with territoriality, escape from potential predators or may be ritualised with reproduction or feeding. It may be exhibited with humans, conspecifics, other animals or with no stimulation.