In the first battle scene, Campbell-Hamish's father-gets his hand cut off after being knocked to the ground. Look at his arm. It is obviously a fake arm, because it just isn't shaped correctly. It has too many bends, is too long, and there are hollow sections underneath the fabric of his sleeves.

I would like to add that Braveheart is my favorite movie though, and Slip-ups like this don't really bother me. I just happened to notice them.