My puppy growled at me the first week I had her after I gave her a bone.
I dont bother her when she eats, have never stuck my hands in her bowl, but after that instance for high value things I did teach her it was something that was shared between us and not a "it's mine I'll growl at you". For example, I eat a bite of steak, I handed her one, then hand her a few more, etc. I hand fed high value things for a little while. She understood if she was nice to me i'd give her more. Never had an issue ever again. I can pull anything out of her mouth or make her drop it.
" Mei vom Majic Forest