Spells are the every-purpose tools of a wizard or witch; short bursts of magic used to accomplish single specialised tasks such as opening locks or creating fire. Typically casting requires an incantation, most often in a modified form of Latin (see Dog Latin), and gesturing with a wand. However, Rowling has revealed that particularly talented wizards can cast spells without the aid of wand, although magic produced with one is generally more precise and powerful. Spells can also be cast non-verbally, but with a magical wand. This special technique is taught in the sixth year of study at Hogwarts and requires the caster to concentrate on the incantation. Some spells (e.g., "Levicorpus") are apparently designed to be used non-verbally. While most magic shown in the books requires the caster to use their voice, some do not (and this may depend on the witch or wizard). Dumbledore has been known to do impressive feats of magic without speaking, such as conjuring enough squashy purple sleeping bags to accommodate the entire student population or during his duel with Voldemort towards the end of "Order of the Phoenix".