Freezing describes the cat’s sudden assumption of a totally immobile posture, usually in response to an environmental or social stimulus. Although a cat may freeze with its body in any position, it is most common for the cat to assume a crouching posture as it freezes. Evidence of emotional arousal is frequently observed in that the senses are usually orientated towards the stimulus which elicited the freeze, with a fixed gaze and dilated pupils. Ears may be orientated pricked towards the stimulus or may be flattened sideways (see negative emotional states) and whiskers may be pricked forwards or pulled back against the face. The tail may be held out behind the body along the ground or more commonly tucked around the body and paws. Muscles are usually tensed so that the cat appears poised.