I'm not sure it's a matter of knowing what the word NO means. Zoey knows what NO means but she just chooses to ignore obeying "NO" when she wants to play bite. This technique below has worked for Zoey to some extent and also what works too is getting down into her face and growling like a big dog and saying NO at the same time. She may try to bite once or twice after I do this but then will run away and stop.