Quote from : Harry Potter and the Order of the Phoenix Book

Don't let Ron see what's on those Slytherin's badges," she whispered urgently. Harry looked questioningly at her, but she shook her head warningly; Ron had just ambled over to them, looking lost and desparate. "Good luck, Ron," said Hermione, standing on tiptoe and kissing him on the cheek. "And you, Harry --" Ron seemed to come to himself slightly as they walked back across the Great Hall. He touched the spot on his face where Hermione had kissed him, looking puzzled, as though he was not quite sure what had just happened.