neutered male cat trying to mate

Question
I currently have 8 cats all are spayed/neutered except for 2 4 month old brothers. One of my neutered male cats, a 2 years old dsh orange tabby named Oscar started humping my other neutered almost 3 year old dlh black/white cat named Sylvester. Oscar has never done this in all the time that i've had him. I adopted him from a humane society in march 2007 when he was 9 months old. Last night was the first and only time that i've seen Oscar do this. Sylvester was laying in the floor and Oscar went over to Sylvester and got on top of him and started grooming him. They do this often where they will wrestle and groom each with one being on top. They are very attached to one another. While Oscar was on top of Sylvester he stopped grooming Sylvester and started humping him. Sylvester kept grooming Oscar while this was happening. I don't think Sylvester realize what was happening. Oscar kept humping Sylvester for quite a while and after a little bit Sylvester started trying to get Oscar off of him, but Oscar wouldn't get off. So i went a picked Oscar up and put him on the bed. After i put Oscar on the bed i turned him on his side and opened his legs to kinds checked down there to see if maybe i could see if something maybe was wrong. From what i could telling nothing appeared to be wrong but Oscar's penis was sticking out so i knew for sure that he was indeed trying to mate and not just to play or anything like that. I was wondering if you maybe had an idea as to why Oscar is doing this? As of right now Oscar hasn't been marking or not anywhere that i can find. I was wondering if maybe the humane society didn't completely neutered? I had thought that maybe he started acting this way because of the 2 4 month old unneutered kitten that i have, but i don't that they are the cause because i adopted them 2 months ago. And last year i adopted a 6 month old unspayed female cat from the pound. When i took her for her checked and exam the vet said that she would be going into heat soon because of easy she took thermometer. The vet had me wait a few weeks before i had her spayed because she was very skinny and barely weighed 5 lbs. Oscar never has tried mating with her or any of my other cats except for Sylvester. Do you think that i should take Oscar to the vet or do you think that he is doing this because of something is is or has happened between him and Sylvester? Sorry for all the questions and long drawn out post but i want you to have some background. Any and all advice is appreciated.

Thanks,
Felicia

Answer
Felicia,

Not to worry! His behavior is common with alot of neutered males. They act in a sexual manner even though they have been neutered. It usually starts about 2-3 years old. It is just a response that some cats have to sexual stimulation. Some cats have a strong 'male mentality' and though they physically can't do anything they mentally can.

Usually the cause for this behavior is that the neutered cat smells a female in heat somewhere in the neighborhood (even if they are inside cats) and react to it, or it could be that one of your young males are coming in heat and he is reacting to that.

I have been told about neutered males that will hump or bite the neck of other cats in the family (as yours is doing) male or female; dogs, peoples legs and arms, and even stuffed animals.

When he does that don't get mad at him or scold him because it's nature and he doesn't understand what he is doing wrong. But also don't pet him because that can get him more stimulated. Try to distract him with food or toys. A pet laser light (from PetSmart, Petco, etc.) is an excellent distraction.

The behavior should stop when whatever is stimulating him stops.

I hope this helps relieve your mind.

Tabbi