The Patronus Charm is a defensive spell that, if performed correctly, conjures a silvery animal form particular to the user. The charm is used to defend against Dementors - where the witch or wizard summons a guardian to shield them. The Patronus is formed of hope and happiness, so that the Dementor feeds on it rather than the caster. In order to cast the spell, it is necessary first to think of a happy memory and then use the incantation, ‘Expecto Patronum’. Used famously by Harry Potter in order to save a future version of himself from Dementors whilst using a Time-Turner, each witch or wizard’s Patronus holds meaning for them, resembling part of their character or occasionally in homage to a loved one. While a corporeal Patronus was strongest, non-corporeal forms could be slightly effective. Corporeal animal form Patronuses can also be used to deliver messages, speaking in the caster's voice.