“So what happens when a wand meets its brother?” said Sirius. “They will not work properly against each other,” said Dumbledore. “If, however, the owners of the wands force the wands to do battle . . . a very rare effect will take place. One of the wands will force the other to regurgitate spells it has performed — in reverse. The most recent first . . . and then those which preceded it. . . .”
