noun
frothing at the mouth
Literally 'foam at the corners of the mouth'; used to describe someone speaking with great excitement or anger, often in the phrase 口角泡を飛ばす.
彼は口角泡を飛ばして議論した。
He argued vehemently, frothing at the mouth.
Means 'to foam at the mouth' in a literal, often medical sense (e.g., seizure), while 口角泡 is more figurative and used for heated speech.
Compound of 口角 (corners of the mouth) and 泡 (foam). The exact origin is uncertain, but it likely arose from the vivid image of someone speaking so passionately that foam gathers at the mouth.