- "A jet of green light issued from Voldemorts wand just as a jet of red light blasted from Harry's — they met in midair — and suddenly Harry's wand was vibrating as though an electric charge were surging through it; his hand seized up around it; he couldn't have released it if he'd wanted to — and a narrow beam of light connected the two wands, neither red nor green, but bright, deep gold... he felt his feet lift from the ground. He and Voldemort were both being raised into the air, their wands still connected by that thread of shimmering golden light."
- —The Harry's and Voldemort's twin wand cores connect[src]
The Reverse Spell[2] (Prior Incantato)[1] was a spell that forced a wand to show an "echo" of the most recent spell it had performed.[1][3][4] An especially rare manifestation of this spell is known as Priori Incantatem.[3][4] It is an unintended consequence of two wands with cores taken from the same animal, duelling each other; the winner's wand forces the loser's wand to reproduce in reverse order "echoes" of the most recent spells performed.[3][4]
Effects
Priori Incantatem
- "The golden thread connecting Harry and Voldemort splintered; though the wands remained connected, a thousand more beams arced high over Harry and Voldemort, crisscrossing all around them, until they were enclosed in a golden, dome-shaped web, a cage of light..."
- —The dome of light, a side-effect of the spell[src]

The cage of protective light created by Priori Incantatem
When a duel occurred between wizards with wand cores harvested from the same creature, simultaneous spell-casting by both parties would trigger a rare, powerful effect called Priori Incantatem.[3][4] Both wands became linked through a single, golden thread of energy.[3] Hundreds of smaller golden beams shot off from this central thread to form a cage around the duellers.[3]
The two wand holders were then forced to compete in a battle of wills.[3] When one wand managed to overcome the other, it forced the losing wand to regurgitate "echoes" of the most recent spells it had cast, in reverse order.[3][4]

The "echo" of Cedric Diggory released by the effects of Priori Incantatem
If one of these spells was the Killing Curse, then a ghostly "echo" of the murdered person could emerge from the killer's wand.[3][4] Such "echoes" retained the "appearance and character" of the deceased person.[3][4] They were able to hold conversations and could remember the events leading up to and following their deaths.[3][4] However, these "echoes" were not ghosts, nor were they considered to be returning the deceased person from the dead[4]; indeed, they could only linger on the mortal plane for a few moments before they faded back into the Beyond.
History

Harry Potter and Lord Voldemort duel in Little Hangleton graveyard
Amos Diggory cast the Reverse Spell on Harry Potter's wand in the aftermath of the Death Eater attack at the 1994 Quidditch World Cup in order to determine whether he conjured the Dark Mark over the campsite.[1]
Lord Voldemort was resurrected by Peter Pettigrew using the blood of Harry Potter in the Little Hangleton graveyard on 24 June 1995. A duel ensued between Voldemort and Harry, during which their wands (which both contained feathers from the phoenix Fawkes) became connected, triggering Priori Incantatem.[3][4] Voldemort's wand was ultimately overcome by Harry's, causing it to release "shadows" of people he had murdered with it: Cedric Diggory, Frank Bryce, Bertha Jorkins, as well as Lily and James Potter.[3][4]
Behind the scenes
- Throughout the film adaptations of the story, there are several instances of two wizards locking spells with one another, presumably for dramatic effect. Although similar to Priori Incantatem, these events did not actually result in a cage of light, nor the release of echoes of past spells.

Arthur Weasley and an unidentified Death Eater duelling, producing an effect similar to Priori Incantatem
- Instances of this include Albus Dumbledore and Lord Voldemort during the duel in the Ministry Atrium in Harry Potter and the Order of the Phoenix (film); a Death Eater and Arthur Weasley in the Battle of Hogwarts in Harry Potter and the Deathly Hallows: Part 2; and Harry Potter (using Draco Malfoy's wand) and Lord Voldemort (using the Elder Wand) several times during Voldemort's Last Stand, also in Harry Potter and the Deathly Hallows: Part 2
- In Harry Potter and the Deathly Hallows: Part 1, during the Skirmish at Malfoy Manor in 1998 Bellatrix Lestrange used this spell on Hermione Granger's wand to learn if she used a Stinging Hex on Harry Potter to make him unrecognisable.
- In the novel of Harry Potter and the Goblet of Fire, Bertha Jorkins' echo appears during Voldemort's duel with Harry, while in the film adaptation, her echo doesn't appear. This is because the character of Bertha Jorkins has been omitted entirely from the films.
Appearances
- Harry Potter and the Goblet of Fire (First appearance)
- Harry Potter and the Goblet of Fire (film)
- Harry Potter and the Goblet of Fire (video game)
- Harry Potter and the Deathly Hallows: Part 1 (Indirect mention)
- Harry Potter: A Pop-Up Book (Mentioned only)
- LEGO Harry Potter: Years 1-4
- LEGO Harry Potter: Years 5-7
- Harry Potter for Kinect
- Harry Potter: The Character Vault
Notes and references
- ↑ 1.0 1.1 1.2 1.3 Harry Potter and the Goblet of Fire, Chapter 9
- ↑ Harry Potter and the Goblet of Fire, Chapter 36 - “The Reverse Spell effect?” said Sirius sharply.
- ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 Harry Potter and the Goblet of Fire, Chapter 34
- ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 Harry Potter and the Goblet of Fire, Chapter 36