Continuity mistake: During CoMC class, after Hagrid coughs, says, "Ta da!" and gestures toward Buckbeak, there is a shot of the students and Hermione's Monster Book of Monsters lies open on the huge rock. In the next close-up of Hermione, her book is closed and partially buckled. When Ron asks, "Hagrid...what is that?" her book lies open again. Books lying near Hermione's change in consecutive shots as well, including the one held by the girl beside Neville.
Picture added by Super Grover