I'm not an expert, but Teddy was the same way at first. I was shocked and irritated because I've never owned a dog who had the nerve to snap at me. When he'd do that, I'd say "NO!" and take his food away from him. I wanted him to know that I gave him that food, and I can take it back just as easy. I started hand feeding him also, to let him know if he's nice, he can eat. I don't know if it is the right way to deal with it, but it worked.