According to the interwebs it is usually a sign of severe physiological stress. Shedding causing vision to be restricted. Overheating, captivity stress. Also with the way their fangs face back if a snake starts this it becomes difficult for them to stop.

It was told it was going to have work for a living like humans

Feels good man.

Yes. Somewhat frequently considering its in stories all over the world

Reticulating spine?

Snakes basically never completely latch on when they bite you unless you're picking them up and fucking with them or it's something like a full grown reticulated python and it's trying to actually eat you. Typically if you accidentally get to close or something the worst you'll get it a quick warning bite which barely breaks the skin if anything. Venomous snakes usually won't even waste venom on you for a warning.

Most snakes want nothing to do with us and won't go near you if you don't go near them. The only exceptions are the ones large enough to consider us potential food or the rare super teritorial species like the fer-de-lance which will chase you just because they're assholes. But the fer-de-lance is honestly the only example I can think of in that second category and is a bit of an outlier.