The opportunity for Hermione to slip the adulterated dragon pox potion into Rodolphus" food or drink didn't present itself immediately. Following her trip to Diagon Alley, she returned to the Dower House to wait patiently for his return. It was yet another night that he didn't come home until she was already in bed. She heard the footsteps down the corridor stop just outside the door to her bedroom again before they crossed into his room. If she needed further proof that it would only be a matter of time before Rodolphus tried to seduce her again, she had it each time he lingered outside her bedroom door.