I was just about to post the same exact question. We have Bella

1 1/2 years old ( 5.6 pounds). Very docile and submissive

. Luigi

(tiny 2.2 pounds) came to live here last month. He is an aggressive little guy. They will start out playing then all of a sudden he is growling like a viscious beast

. In the beginning Bella ran from it now she is fighting back. She also is possesive of the toys. I have even watched her take them one at a time and put them on the couch. Luigi can't get up on the couch he is so small. Like you I don't know if it is playing or fighting. The vet told me that Luigi will not stop his aggressivness until Bella draws blood

. That is a little scary to me, although she has made Luigi yelp a few times it still continues. Oh but on the flip side they will lay down and sleep together and lick each other. I am confused. If anyone has any thoughts on this I would also appreciate it.