Reverse Spell Incantation Prior Incantato[1](PRI-or in-can-TAH-toh) Type Charm Hand movement Hold tip of wand to targeted wand Light Gold[2] Effect Shows the previous spells cast by a wand

The Reverse Spell (Priori Incantatem) is a magical phenomenon that can occur when two wands which share the same source for their cores are forced to compete in combat. It is sometimes referred to as the "reverse-spell effect". It can also be induced by analytical spells, like an extension of the Prior Incantato spell.

During a wand duel, a simultaneous spellcasting by both parties with twin wand cores will trigger an effect whereby both wands are linked through separate threads of spell energy. The two wand holders then compete in a battle of wills, in which the loser's wand is forced to display in ghostly form the spells which had been cast by said wand, in order of most recent to least recent. If any of those spells are Killing Curses, the victims will appear in ghost-like form. These echos are capable of holding a conversation with nearby living beings.

When the spells come into contact they send out a seismic pulse which has enough force to knock onlookers from their feet. When the spells meet, they intertwine, making it difficult for either caster to break the connection. A spell-like residue falls from the core of the connection, possibly representing the wills of the casters and the energy of the incantations. A dome effect occurs during the connection. This done effect keeps any intruders from attacking either wizard or witch. The sound of the connection is similar to electrical arcs.

The effect is similar to the spell Prior Incantato (but this spell does not need a wand connection), which causes the targeted wand to recall its last spells.

The only widely-known instance of Priori Incantatem came about in 1995, at the graveyard in Little Hangleton, when Harry Potter first duelled with the resurrected Lord Voldemort. The two wands in question both had a phoenix feather at their core from Fawkes, pet of Albus Dumbledore. Due to rarity of twin cores ever meeting up with each other, this phenomenon is also rare.

Priori Incantatem rarely ever happens when two opponents forcibly use their wands in battle. The reason for the case of the 1995 duel between Harry Potter and Lord Voldemort are the shared wand cores; since the wands recognised each other as "brothers", they refused to destroy each other. When spurred on, however, the dominant (Harry's) forced the submissive to regurgitate its spells.

A possible etymology for Priori Incantatem is prior incarnation, refering to its effect of "regurgitating" previous spells. However, the Latin literally means "prior incantation" or "previous spell"; more literally, an incantation is a spell spoken aloud.

Arthur Weasley and an unidentified Death Eater duelling, producing an effect similar to Priori Incantatem.