The sixth years' frustration builds as they learn that the March 1st [Hogsmeade] trip is cancelled and [Apparition] lessons continue to prove challenging.
Ron awakes on his birthday and starts opening his gifts - but unwittingly eats two [Chocolate Cauldrons] laced with [Romilda Vane]'s [love potion], and gets into a brief fight with a disbelieving Harry.
Professor Slughorn whips up an antidote for Ron's [love potion], but in the ensuing celebration Ron is also accidentally poisoned. He is spared from death only when Harry thinks to grab a bezoar from Slughorn's bag and shove it down Ron's throat.
Chapter 19 - "Elf Tails" - In which Harry discusses Ron's poisioning with the Weasleys, Hagrid tells Harry that he overheard Dumbledore and Snape arguing, McLaggen accosts Harry to ensure he can play in Ron's place in the upcoming Quidditch match, and Harry finds that Ron has been avoiding Lavender. At the Quidditch match (with Luna commentating!), McLaggen grabs a beater's bat and cracks Harry's skull. Finally, in the hospital wing, Harry summons Kreacher and Dobby and orders them to tail Malfoy and figure out what he's up to.
Visiting Ron in the Hospital Wing
Harry, Hermione, and Hagrid leave the hospital wing talking about the possibility of Hogwarts closing, and Hagrid lets slip that [Dumbledore] has argued with Snape. Filch then shows up and tries to give a detention to Harry and Hermione, but Hagrid gets them off.
Malfoy, McLaggen, and Lavender All Annoy Harry