We have 3 cats - a 17 y/o female (Alex), a 2 y/o male (Chico) and a 2 y/o female (Lulu). The young ones were spayed / neutered when they were under 6 months. The 2 young ones are best friends - they get along really well, and groom each other - it's cute to watch. They are all indoor cats.
Anyway, my husband recently took them all into the vet - separate visits, since we have only 1 carrier. Chico was the last to go. For a few days after the appointment, I noticed him biting the back of Lulu's neck- almost like he was trying to mate with her. He tried it a few times. Of course, she'd have nothing to do with him. It seemed really odd to me - I mean, he was spayed almost 2 years ago. The vet gave him some sort of injection when he was there - my husband said it was for respiratory - my father said maybe it was 'kitty viagra'! He was also very affectionate with us - slept with us all night for a couple of nights, that kind of thing.
Anyone else ever have this kind of situation? He seems to have calmed down this week - back to normal and spends his time watching the birds and sleeping.