A baby fetus has a heartbeat after ten days. The liver has 300 functions. Birthmarks can be hereditary. Nobody knows why we have blood types. Sea coral can be used in bone graft surgery. It's impossible for a contact lens to get stuck behind your eye. There are at least nine useless organs. The appendix isn't one of them. There are absolutely no muscles in your fingers. Some scientists believe the gut has a second brain. Teeth can survive lava. You have taste buds in your ears. Nobody has a clue how many muscles the human body has. There are seven types of twins. Men and women experience different symptoms before they have a heart attack. When a person gets a kidney transplant, their old kidneys are usually not removed. There is only one muscle that can't get tired. You can survive without an intestine. It is possible to survive with 90%% of your brain removed.