Where does the saying foam at mouth come from?

The saying "foam at the mouth" likely originated from observations of people and animals suffering from rabies.

Here's why:

* Rabies: Rabies is a viral disease that affects the central nervous system, leading to severe symptoms like agitation, confusion, and hydrophobia (fear of water). One of the most prominent and disturbing symptoms of rabies is excessive salivation, which can lead to the appearance of frothing or foaming at the mouth.

* Historical Context: Before the advent of vaccines and modern medical understanding, rabies was a common and often deadly disease. People would have witnessed its effects firsthand, including the distinctive foaming at the mouth.

* Figurative Meaning: Over time, the phrase "foam at the mouth" became a metaphor for extreme anger, rage, or excitement. This likely stemmed from the association with the violent and irrational behavior seen in people suffering from rabies.

While the saying is rooted in a serious medical condition, it has evolved into a common idiom to describe intense emotions, often used in a humorous or exaggerated way.