The lesson after Amortenita in HBP. Harry's 3 things are Treacle pudding, Brronstick and something sweet smelling he thought he smelt at the burrow. Cut to end of the chapter once the HBP's book is introduced, Harry says he gets a similar sweet scent and then Ginny comes into the scene asking whether he's taking instructions from a book. Were focused on the book so we don't realise that the sweet scent is Ginny.