Muggles' Guide to Harry Potter/Magic/Flying

Muggles' Guide to Harry Potter - Magic
Flying lessons
Type	Class
Features
First Appearance	Harry Potter and the Philosopher's Stone

Overview

The subject of flying is taught by Madam Hooch to the first-years at Hogwarts.

Extended Description

Flying is done using brooms; we are led to believe that it is not possible for a wizard to fly without a broom or some other charmed device (e.g. a flying carpet, though those are currently not allowed in England) or animal (e.g. a Thestral).

One of the rules at Hogwarts is that first-years aren't allowed to posess brooms. This rule was bent for Harry, though: in his first-ever flying lesson, Professor McGonagall sees that he is a natural flier. As a result, Harry was recruited to the Gryffindor Quidditch Team, as Seeker, and was given a Nimbus 2000.

Once his natural ability has been discovered, there is little that Madam Hooch can teach him; his flying lessons are taken over by Oliver Wood, the captain of the Quidditch team, and Harry has no further lessons with Madam Hooch. We must assume that lessons continue for the other students, however.

Questions

1. We are led to believe that flying is only possible with the use of an object (broom, Sirius' flying motorcycle, Mr. Weasley's flying Ford Anglia), or with the assistance of a flying creature (Thestral, Hippogriff, Dragon). How is it that Voldemort, and later Snape, seem to be capable of unassisted flight in Harry Potter and the Deathly Hallows?