My garters at least have picked up the habit of not moving some of the time when I touch them. They don't bother to move for a minute or two while I pet them since they've decided they don't really care I guess - freaks me out every time. But equally often they're all the way across the tank before my hand gets anywhere near them and more often than either of those, they're busily checking if I have food. I don't know that the behavior is normal for your corn snake, but it's at least definitely possible for colubrids that are acclimated to humans. She might have thought that she was well enough hidden and was just fine with where she was. They don't have the head shyness that ball pythons do.