Medieval/fantasy book appropriate spanking implement?

I’m hoping someone has some niche knowledge to help me. I’m writing a fanfiction with a spanking scene (it’s a discipline thing more so than a sexy thing, punishment not funishment) but I’m having a hard time thinking of an appropriate implement for it because it’s based on a fantasy book that sort of takes place in a mid-medieval time period and I want the spanking implement to match that if possible.

The other issue is the spankee is a magical assassin (technically i should say wetboy but I don’t think anyone knows what that is lol. Or maybe everyone who reads fantasy knows. Who knows.) and hes fought and killed a bunch of people so I have to assume he has a fairly high pain tolerance, so I’m also looking for something that would hurt a lot.

Does anyone happen to have an idea for a potential implement that would work for that?