We asked him about the bird, and he cleared it up: Draco, while faking injury from Buckbeak, draws a picture of Harry being electrocuted by a lightning bolt; he then folds it up like so and it actually flies over to Harry, who is less than pleased upon receiving it.
Also note the rings Malfoy, Crabbe and Goyle are wearing; they are tiny silver snakes, and the kids also have tie clips. A touch from Cuaron, only these Slytherins wear the ornamentation; it was decided amongst the kids the jewelry was a gift from Lucius Malfoy.
Also, look where the kids' textbooks are open, and note why Draco would even dare to pass a note so openly. This is Lupin's class that Snape takes over, and they are indeed reading about werewolves.