When the T-1000 and Arnie meet in the back hall of the Arcade in the mall, and Arnold tags him for the first time - watch the "bullet hole" closely. It's only for a second. You can see it moving, as part of his SHIRT! This is obviously how they pulled the effect off (as a matter of fact, I've seen the costume up close and it's pretty cheesy!) Anyhow, if the impact is as deep as it appears, the hole shouldn't move.