I had a question about weird cat behavior but I just realized that I am guilty of feeding my neighbor's cat and how bad that potentially could be. We have new neighbors next door and we haven't actually me them. The woman is the sister in law of the owner of the house who we don't get a long with so there wasn't a big incentive to get to know them... They went away for the weekend and left their cat at home. He kept coming over to our house so I fed him. Guilty. Weeks later he keeps coming over so I keep feeding him. It never dawned on me that he might be on a restricted diet, have health issues or that it was just wrong of me to feed someone else's cat! Yesterday after I fed him and he stayed around like he wanted to be petted. I petted him and he hissed at me. Then he head butted me so I thought he wanted to be petted but he hissed at me again. Why would a cat head butt me and hiss at me too?