Tocho is a two year old male, and since we got him about a year old he has contantly picked on our other cat, Meursault. I notice it's always him who starts it, but he never tries to hurt her. He just chases her until she turns around and hisses and scream at him. Then he just lets her go. I don't think it's any hormonal thing, since they've both been altered. I'm not sure whether he's just trying to play with her or wants to assert his dominance.