Anger is a natural emotion that every human and many non-human animals experience. Mild forms of human anger may include displeasure, irritation or dislike. When we react to frustration, criticism or a threat, we may become angry - and usually this is a healthy response. Anger may be a secondary response to feeling sad, lonely or frightened. When anger becomes a full-blown rage our judgment and thinking can become impaired and we are more likely to do and say unreasonable and irrational things.