Artifacts?

[skalnik]

I have 2 STL files: http://cloud.mikeskalnik.com/0a2N2V1C0a26 (a terrible person model with a bent arm) & http://cloud.mikeskalnik.com/3p0R2b0v1Q09 (same model but with a straight arm). When I subtract one from the other, I get some odd results with some artifacts:

[skalnik]

I'd love to solve this soon. I don't have the know how on my own to do this, but I'd love to pair or give it a shot given some guidance.