You can bite into lead. You can't bite into gold, silver and bronze. That's why it used to be a test for fake coins. If the chips are bite marks, the metal's really low grade. Biting into Gold and Silver is even easier.
Yep, I've since looked it up, and it's apparently the most malleable metal, with Silver coming second. To be fair, Lead is pretty malleable, too, and you can leave bite marks in it if you put it in your mouth.