What does frothed at the mouth mean?

The expression "frothed at the mouth" refers to becoming extremely angry or agitated, often to the point of spittle (saliva) being forcibly expelled from the mouth during outbursts of intense emotion or stress. It suggests a loss of control and heightened agitation similar to what may occur with rabies infection, where uncontrollable muscle actions result in foaming at the mouth. Using this phrase emphasizes the extreme and irrational nature of one's anger, implying extreme levels of frustration or outrage.