Ferula is a spell that first occurred in Harry Potter and the Prisoner of Azkaban, the third book in the Harry Potter series.
Professor Remus Lupin cast this spell on Ron Weasley to help mend his broken leg while they were leaving the Shrieking Shack with Sirius Black, Hermione Granger, Harry Potter, Peter Pettigrew and an unconscious Severus Snape. The spell is described as "bandages spinning up Ron's leg, snapping it tightly to a splint". Presumably, the bandages and splint appeared from nowhere.
--Optimistic 02:41, 27 February 2007 (UTC)