My wife is in the medical field and has seen someone with lockjaw. Awful. They had to have muscles from the legs taken out and grafted to their jaw to get even partial movement back, but they will never be the same.
It is not something to mess with. Supposedly the key is if you have a puncture wound or a deep cut, need a shot asap. A light scratch that can be cleaned enough to get the rust out, prob OK.
My arse would be in the car and on the way to the doc to be safe though.