Sarah was ready for charms class, and her reflection in the mirror had told her that she was ready too! She had to go to great lengths on her appearance, something which she did not give a hoot about, for the professor.
She walked and waved at all, "hello professor!" she said. A survey of the surroundings brought Sarah's brain into motion. She was meant to stabilise the chairs if she wanted to sit down. "Immobulus" she casted on the one chair and it grinded to a halt. Sarah sat down on it, and then regretted doing the Immobulus charm, she would have preferred to be sitting on a moving chair.