I think worms are pretty well adapted to being pulled into smaller pieces. I remember many times as a kid trying to collect worms from the soil and accidentally pulling them in half when I went to pull them out. The part of the worm with the "head" will continue living even if you chop the "tail" end off multiple times. At first it sort of bothered me too, but I soon got use to it. At least the worms are being used to keep your snakes healthy instead of being stabbed onto a fishing hook and cast into a lake (no offence fishing-people, I've fished with worms many times myself).