Foaming at the mouth is an idiom that has been in use for hundreds of years. We will examine the meaning of the common idiom foaming at the mouth where it came from, and some examples of its idiomatic usage in sentences.
Foaming at the mouth describes being in a rage or being very angry. The phrase foaming at the mouth has been in use for quite awhile in a literal sense; it is a symptom of rabies. Rabies is a virus that is fatal if untreated, and often fatal even if treated. The symptoms of rabies include aggression, bizarre behavior, hallucinations, muscle spasms, etc. One of the symptoms of rabies is foaming at the mouth, because the victim cannot swallow properly. Therefore, foaming at the mouth is equated with rage. It is unclear exactly when the expression foaming at the mouth became a idiom, though it has been one for at least several hundred years. Related phrases are foam at the mouth, foams at the mouth, foamed at the mouth.
He was shouting and foaming at the mouth. (Manchester Evening News)
Schallenberg added that “it won’t be possible to solve the Middle East conflict while foaming at the mouth.” (AP News)
So we met the next day and of course I was foaming at the mouth with this laundry list of things I wanted to do — outdoor festivals and markets and fairs and concerts and private events. (Lexington Herald Leader)