Gavin (my yorkie) was neutered before we got Molly. Molly was 2 yrs old when she came and was not spayed. She would demand Gavin to satisfy her and he would try and make her happy. I only saw him do the motions with no obvious signs of arousal. He weighs about twice as much as her but never seem to hurt her. I would always try and break it up but when Molly went into heat she was obsessed with Gavin. Poor Gavin had to be rescued from her! Molly doesn't seem to "stand" for him anymore. (she was spayed in November) She humps his head though! (only when he is chewing on something :roll: ) I think it's a dominance thing or maybe she's just mad that he's not paying attention to her. Who knows!