Doug, horses do not chomp at the bit. If they did, their teeth would break, and horses are smart enough not to break their own teeth. Instead, they merely champ at the bit. That means playing at it in their mouths, pushing it around with their tongues, and sometimes making as much noise as they can. They've been doing that since there were bits to champ at. Descriptive dictionaries are now mixing up these two words but there is valid reason to keep them separate.