In my expierence it is pretty easy to tell whether a fish is snagged of not. Snagging a fish in the head is just as bad as snagging one in the tail. Bottom line is if the fish doesn't bite your bait then it is snagged. I've seen many fish hooked at the bottom of the jaw, with the hook clearly outside the fishes mouth. How can you say that is was biting? Was it biting on the line? As far as I'm concerned, lining a fish is just another way of snagging!