Does Marie really want to know which of her shoes smells better, or does she just like degrading this slave by making him inhale her shoe scent? It's probably a bit of both as it amuses her to know that while she is out shopping her male pet is at home kneeling by her toilet smelling her shoes. When she comes home she even permits him to smell the pair she has been wearing all day, letting him enjoy some freshly generated foot stench.