Duvernoy's gland (thought this was a good read)

[ConcinusMan]

A little nip to warn off predators is different than a feeding response bite.

Exactly. The only time I've ever had a reaction (rash-like redness, itchy burning sensation) is when my hand was mistake for food and the snake refused to let go. I think it's the struggling and the snake's determination to swallow that which is struggling to get free, that the Duvernoy's gland secretions come into play. Simply washing the bite area thoroughly and using an antiseptic on the wound was enough to stop the symptoms. One should do that anyway if the skin is broken.