Chewing gum stays in your body if swallowed. That would mean that every single person who ever swallowed gum would have evidence of the gum in the digestive tract. No such evidence exists....ever had a colonoscopy????
Hats keep in heat. Sorry, if mom told you this she meant well but 40 to 45" of your body heat doesn't escape out of your head like a boiled kettle.
Nails and hair continue to grow after you die. Nope, the myth comes from the fact that skin recedes form a dead body, making nails and hair appear longer.