Hmmmmmmmmmmmmmmmmmmmm

An animal's tail is an extension of their spine. That's why you don't pull the tails of cats. I bet it hurts them because it's a sudden force pushed onto the part of their body that literally lets them stand up.

Theory disproved, but you were on the right track

Cool

I think it hurts so much because the tail is so weak.

It's not what you think because most reptiles don't have one. So I don't know.