Ziggy definitely thinks he is playing (and cats can act kittenish long past a year) I THINK Zuzu is playing too (she's hiding under things so her body language is harder to see) but Ziggy is being too rough and that is why the hisses. Definitely not a full fledged cat fight, but not fun for you to listen to. If he is distractable, see if you can get him playing with something else. Since this is play, when he is tired out he won't bother ZuZu any more. Try a toy called Cat Dancer. My cats go wild and will play with this as long as I let them. It's simple, cheap and entertaining for the cats, but requires human participation.
Dr. Seuss~DLH (brother's cat)~June 2007-
Misty~DSH (my cat & Mooby's mom)-?-
MooBoots(Mooby) ~ DMH(Mom's cat)~July 21, 2008-
Sunshine~ Golden retriever X white german sheperd (Dad's dog)~October 24, 2008-