I got 2 female rabbits in October at 3 months old. They are from the same litter so they have been together since birth. They have always gotten along really well. I got them spayed 2 days ago and have noticed they are both bitting each other’s butts. I have seen them bite each other‘s butts a couple times before they got spayed but it was rare. So far it has not lead to any other aggressive behavior. What does this mean?