Rabbits, you know, have scent glands under their chins which they use to mark the things that belong to them. At this point, I don't suppose there's any doubt in the world as to who Bleu really belongs to. She and Fiachra might not be what you'd call a traditional couple. It's a toss-up as to which one of them is more fiercely independent, and they certainly enjoy the freedoms that they afford each other. At the end of the day, though, neither of them have any doubt to whom they belong.
Besides, it gives them a nice excuse to cuddle for a while, and to look adorable.