Audio problem: Ron's "let's go" sounds different before and after the time travel.
Continuity mistake: When Sirius and Lupin cast a spell to change Pettigrew from a rat and back into human form, he is fully clothed, as was Sirius when he changed from a dog. Later, when Pettigrew changes back into a rat to escape, his clothes remain behind as he shrinks.
Continuity mistake: Hermione's blue shoes look different in a couple of scenes, from when they were walking down to Hagrid's hut compared to right after Lupin attacked them.
Continuity mistake: Hermione and Ron's feet seem really close together after Buckbeak's "execution", but after Scabbers bites Ron their feet are suddenly much further apart.
Continuity mistake: When Harry drops the Monster Book of Monsters, the scraps of torn paper are already lying around Harry's feet before the book hits the floor.
Chosen answer: It's not known what it is. It is left to the audience's imagination of what exactly is in the room or what some witch or wizard was doing in there. This is only meant to be a humorous bit and is unrelated to the plot. It didn't happen in the book.
raywest ★