Everyone's mom or grandma has a saying that always ends up sticking with them. It may be a wise saying, a humorous one, or simply to scare a child from doing certain things. My grandma (savta), would always tell me, er, more like yell at me, "Not with your teeth!"
I use my teeth for everything: to open stuff, to tear hanging thread off clothing, to hold something while I am doing other things with my hands, to open bottles... They're a great tool. If savta catches me, she squints her eyes and gives me a little smack.
Once, when my brother and I were in our early years of grade school, I learned exactly why you shouldn't ever use your teeth. Mom, please forgive me for telling this story.