““Harry,” said Hermione, “how are we going to get out of here with all those dementors outside the door?” “Patronuses,” said Harry, pointing his wand at his own: The stag slowed and walked, still gleaming brightly, toward the door. “As many as we can muster; do yours, Hermione.” “ Expec--Expecto patronum ,” said Hermione. Nothing happened. “It’s the only spell she ever has trouble with,” Harry told a completely bemused Mrs. Cattermole. “Bit unfortunate, really…Come on, Hermione…” “ Expecto patronum! ” A silver otter burst from the end of Hermione’s wand and swam gracefully through the air to join the stag.””