Will a kingsnake shake its tail?

Yes. The King snake will shake it's tail at you, sorta like a rattle snake shakes it's rattler. I am pretty sure it's not like a dog wagging it's tail, saying "hey I'm happy/exited/nervous/.

It is a warning. When the snake shakes its tail it is simply telling you "I'm not in the mood for whatever you're about to do", "so either do it and risk getting bitten, or pooped on, or wait until I am in a better mood, and not shaking my tail at you!"

That's what I've got. If someone else has a better answer, so be it.