You may have already answered this: I'm not completely awake. (It's ninish my time on a Saturday...) Is Sunny altered? How about his sister? Male cat biting female cat's neck is classic feline mating step, although it can be a dominence thing, too.

I've been amazed at how my two behave together. There are times they do fight (rarely thank heavens) and many more times they ignore one another, but their 'play fights' (not quite a daily occurance) seems awfully real to me until I noticed how it really just seemed to let off steam for the both of them. Sorry I can't explain the difference between real fights and play fights here: something in the tones of their voices. If it starts getting to me I yell out, "Okay, kids, play NICE" and things [usually] quiet right down. This is no explanation, is it?

Good luck. What's the situation like now?