Rowling has described death as the most important theme in the books. Consequently, as Dumbledore states in "Harry Potter and the Goblet of Fire", there is no spell that can truly bring the dead back to life. While corpses can be transformed into obedient Inferi on a living wizard's command, they are little more than zombies with no soul or will of their own. However, there are some methods of communicating with the dead, though with limited results. For example, all Hogwarts headmasters appear in a portrait when they die, allowing consultation by future generations. It is also possible through the rare Priori Incantatem effect to converse with ghost-like "shadows" of magically murdered people. The Resurrection Stone also allows one to talk to the dead, but those brought back by the Stone are not corporeal, nor do they wish to be disturbed from their peaceful rest. Throughout the series, this limit is continually mentioned, and wizards try to transcend it at their own peril.