The external expression of anger can be found in physiological responses, facial expressions, body language, and at times in public acts of aggression. The rib cage tenses and breathing through the nose becomes faster, deeper, and irregular. Anger activates the hypothalamic–pituitary–adrenal axis. The catecholamine activation is more strongly norepinephrine than epinephrine. Heart rate and blood pressure increase. Blood flows to the hands. Perspiration increases (particularly when the anger is intense). The face flushes. The nostrils flare. The jaw tenses. The brow muscles move inward and downward, fixing a hard stare on the target. The arms are raised and a squared-off stance is adopted. The body is mobilized for immediate action, often manifesting as a subjective sense of strength, self-assurance, and potency. This may encourage the impulse to strike out.