based on photos of rescues I've seen snakes have a good ability to heal. I think you would have to do more than just damage a scale. I'm guessing it would be similar to a person in that they'd have to take out a significant chunk of flesh to leave a scar. Unless its a "pedigree" type snake then a small scar prolly isn't a big deal. We all have a few.

In/out of enclosure feeding argument aside, I think that minimizing the obstructions in the eating area is a good idea. This prevents tempting the snake to strike from odd angles. I try to arrange things so the snake and mouse start in their corners (literally), then I ring the bell and yell "fight!", and usually the mouse walks over to the snake's mouth, pries it open, and forces his head in. Ok, maybe I'm exaggerating. But, starting the snake in the corner makes it almost certain that the mouse will walk straight up to it allowing a nice clean strike. Except for a couple of times, mine only has to strike a distance of 2 inches or less and, often, only an inch or less. I've found that any strike that lands in the forward half of the mouse tends to leave the mouse's head pinned very close to the coils, depriving it of the room necessary to turn its head to bite.