Frothing mouth is an expression that describes a seething or boiling anger or madness. Some of the most commonly used synonyms for this expression are rabid or foaming mouth, which are often used to describe a person or an animal that is in a state of intense rage or frenzy. Other synonyms that can be used include wild-eyed, frenzied, crazed, or even berserk. All of these words are used to convey a kind of uncontrolled, irrational behavior that is often associated with anger or madness and can be observed in humans or animals. The synonyms for frothing mouth often paint a vivid picture of someone or something that is in a state of extreme agitation.