My fiance and I have just adopted a new kitten who is 5mo and is a playful and energetic kitten. We have a 5yo Siberian cat named Percy who has always been extremely social and playful as well. Percy, lately, has been playing VERY rough with the kitten. The kitten will even whine and cry out, but he never runs away in fear from Percy or hides from him. In fact he is constantly trying to nuzzle up and walk next to him. There is NO hissing or growling, no ears back and no one is getting all puffed up. Is this normal? Should I be concerned by how rough Percy is being?