Chapter 7 - "Mudbloods and Murmures" - In which Harry begins Quidditch practice, words are exchanged with the Slytherin team, Ron's spell backfires, Harry and Ron serve detention, and Harry hears a voice.
Start of Classes
The second years enter for Defence Against the Dark Arts, where Lockhart gives them a quiz - on himself. He then unleashes Cornish Pixies, fails to control them, and runs out, leaving Harry, Ron, and Hermione to take care of the creatures.
Quidditch Practice Interrupted
[Oliver Wood] leads the [Gryffindor Quidditch team] through an exasperatingly boring lecture on strategy, and then out onto the [Quidditch pitch], where Ron, Hermione, and Colin Creevey are sitting, for the start of practice.
With the [Gryffindor Quidditch team] finally ready to begin practice, they are interrupted by the [Slytherin team], led by Draco Malfoy. Malfoy, rude as ever, insults all of the Gryffindors and calls Hermione a [Mudblood] - prompting Ron to jinx him. The jinx, though, backfires, and Ron begins belching slugs, so Harry and Hermione drag him away.
Slugs at Hagrid's Hut