To be beside oneself with uncontrollable anger; to be enraged.
Example: This person in front of me was driving way too slow, so I honked at them. Well, that didn’t help things, because after I honked, the driver came to a stop, got out of his vehicle and then started yelling at me. He was furious! Yes, I would say he was foaming at the mouth. He must have been having a bad day.
In other words, the driver was very angry.
The Origin Of ‘Foaming At The Mouth’
This phrase likely originates from a virus called rabies, as it can cause literal foaming at the mouth for the animal that’s infected with it. Rabies is a deadly virus that both humans and animals can catch. A bite from an infected animal, like a bat, is usually how this virus spreads. One symptom of rabies is that it makes swallowing very difficult. Consequently, saliva builds up and there is a “foaming” at the mouth.
This expression is at least over 400 years old. For instance, in 1601, William Shakespeare, a famous poet and playwright, used this common expression in the play Julius Caesar:
“He fell down in the market-place, and foamed at mouth, and was speechless.”
- That dude is so angry, just look at him; he’s foaming at the mouth and throwing things around, we should probably leave before he catches sight of us.
Note: There are times when a phrase’s origin is unclear. If that happens, what is usually provided on a page are the popular or plausible theories that are around that talk about how a phrase may have originated. If not that, then I’ll typically try to find the earliest quote that I can of an expression being used in writing. These generally come from old newspapers, books, or poems.
The quotes are meant to give you an idea on how far back in history the expression goes. So, for example, if I quote a book from 1600 because it uses a certain idiom, then it’s at least that old.