"I think...Harry, I think I love her." -- Ron Weasley
Harry gives Slughorn a bezoar instead of an antidote in Potions class, then asks him unsuccessfully about Horcruxes. The sixth-years then have their first apparition lesson, where Harry overhears Malfoy saying Crabbe has been acting as his lookout, and Harry starts watching him using the Marauder’s Map. Then, on Ron’s birthday, Ron accidentally consumes Romilda Vane’s love potion and Harry takes him to Slughorn to get an antidote; there, Slughorn gives Ron some poisoned-laced mead and Harry saves his life with a bezoar.
Calendar and Dates
The chapter begins the day after Harry's lesson with Dumbledore, which means Tuesday, 7 January. We then skip forward to what seems to be a Saturday at the beginning of February, likely either the 1st or 8th. For the end of the chapter, we of course jump to Ron's birthday, which we know to be Saturday, 1 March - the only hardfast date in the book so far. Somewhat uniquely, this fits the calendar that has students taking the Hogwarts Express on 1 September. It's wonderful when these things work out.
Interesting facts and notes
The usual sense of a "birthday surprise" would be a surprise gift, not accidentally being fed candy spiked with love potion, then poisoned mead...
Meanwhile, the Hogwarts library had failed Hermione for the first time in living memory. She was so shocked, she even forgot that she was annoyed at Harry for his trick with the bezoar.
A little way to his left, Ernie Macmillan was contemplating his hoop so hard that his face had turned pink; it looked as though he was straining to lay a Quaffle-sized egg.
They were temporarily detained by Peeves, who had jammed a door on the fourth floor shut and was refusing to let anyone pass until they set fire to their own pants.
Frustration was running high and there was a certain amount of ill-feeling toward Wilkie Twycross and his three D's, which had inspired a number of nicknames for him, the politest of which were Dogbreath and Dunghead.
Friends they might be, but if Ron started calling Lavender "Lav-Lav," he would have to put his foot down.