About a month ago or so, my cat (who is just under a year old) started hissing when you wouldn't normally expect a cat to hiss! It was fairly infrequent in the begginning, but now, when he gets crazy and tears around the house he hisses as he goes!! Usually it happens when he stops to take a breath...he'll pant heavily and hiss while he's panting. It's so weird. I don't feel that he's being aggressive. I think he's just entertaining himself. I just want to know if there is anyone out there who has experienced something similar, or knows if there could be something wrong with him. I've never heard of such a thing before.