“When I was little, my parents used to tell me that if I bit my nails, I’d get worms in my stomach. But, I never did, so it’s okay. But it’s one of those things parents tell you to discourage you from doing bad things.”
Sometimes parents seem pretty desperate to discourage bad habits. As a child, I think this would have information deterred me from biting my nails. When I was young, I really enjoyed eating raw tomatoes. For some reason, this really bothered my mother who told me in graphic detail how parasites living on an uncooked tomato could bore their way through my intestinal tract and come out of my bottom. I am still hesitant to eat uncooked tomatoes to this day.
The idea that she would get worms from chewing her nails may be influenced by the fact that nails are known to carry many different species of bacteria. Since kids are constantly putting their hands into their mouths, parents would find it necessary to scare them into stopping, or teaching them to clean their hands often to prevent them from becoming ill.
When we hear about horrible things like this as a child, they really stick in your mind even after you’ve grown up even if you’ve learned otherwise. Parents hope to discourage bad habits from forming by slightly scaring their children. It makes sense why many of the folktales that the Brothers Grimm collected were so grim: so the cautionary tales children heard would stick with them.