As February progresses, [Harry] keeps checking the [Marauder's Map] to try to find [Malfoy], with a maddening lack of success.
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].
With [Ron] under the influence of [Romilda Vane]'s [love potion], [Harry] thinks quickly and leads [Ron] to [Slughorn]'s office, in hopes of getting an [antidote].
[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
With [Ron] passed out in bed in the [Hospital], the [Weasleys] sit around and discuss his poisoning and its potential relationship to [Katie Bell]'s cursing.
[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
Upon returning to the [common room], [Harry] sits alone and thinks about [Snape] and [Dumbledore], until [Cormac McLaggen] shows up and starts trying to talk [Quidditch].
As time passes, news of [Ron]'s poisoning gets around and [Harry] keeps trying to spot [Malfoy] on the [Marauder's Map], while [Cormac McLaggen] and [Lavender Brown] constantly pester [Harry] to discuss [Quidditch] and [Ron], respectively.