Since the Wolfsbane had to be ingested each of the six days leading up to the full moon, and on the day of, Remus granted Draco access to their Floo, and planned for him to stop in the Saturday before the moon. Remus’ mistake was that he forgot to mention to Hermione that Draco would be stopping by, and of course subsequently forgot himself. On Saturday, Draco stumbled through the fireplace in their sitting room witnessing a scantily dressed witch perched on Remus’ lap, his mouth covering one of her nipples through her thin camisole.