Your roommate Stella has an obsession with the smell of female feet. She’s managed to keep this secret from you and your other roommate.
When she believes she’s home alone, she indulges in the scent of your roommate’s shoe. Stella in heaven until she spots you, shrunk and alone next to the other shoe.
It seems you’re carrying the scent of your roommate’s feet on you, and Stella absolutely loves that.