Confession Time!!

[Archimedes]

It's still a threat response. As big as the bigger species are, we still look much bigger, and like something that might wanna take a bite out of them if given the chance. So they prefer not to allow that chance, and they come out with their guns a-blazin'. If they learn that the defensive reaction is the way to avoid handling, they'll begin to use that as their advantage to keep the big scary two-legged from bothering them. That's why acting with confidence is so highly recommended-- the snake will figure out over time that their huffy-puffy fits don't disturb you, and they'll resign themselves to the handling.