SMB3 producer, Shigeru Miyamoto, says the Chain Chomp was inspired by a neighbors dog. He would go on peaceful walks only to be interrupted by a fearsome hound chained to a post. Despite knowing he was safe at a distance the dog was terrifying.
The Chain Chomps can be defeated by a shell, hammer or star but realistically it’s better just to walk on by like you would with a dog on a chain. Don’t linger; when the level timer reaches 160 the Chains break and you don’t want to be around when that happens.