Sorry need more good awswers about maii dog..?!?

just a minute ago i walked into the kitchen and he started to growl and bark at me when i didnt even do anything, and a 1 hour before this happened he sat on my lap and waggged his tail happily does anyone know why he did that? he is very young my grandfather found him as a pup, and when he was put in his cage he kept growling and barking at me