It’s the quantity. And also, by the time you’ve filled a cup of spit, it has cooled and dried a bit, maybe even breaking itself down, resulting in an increased viscousity, giving it a very unpleasant mouthfeel.

I had some oral mucositis that caused some excessive saliva production. There was one time I accidentally swallowed a mouthful of it, it immediately caused me to vomit.

Fluids that exit the body is like this. Only exception is blood from your own kin and tears. Anything else gets very dirty once out of body. Sweat, urine, vomit etc

Spit in a cup and drink it and watch how your peers react.

Freshness?