The Darkstalker Files
Shifting is the Werewolf ability to transform from a humanoid to wolf or vice versa. For regular wolves, shifting is both natural and painless. For a werebeast, however, the process can be both traumatic and excruciatingly painful.
Shifting is usually voluntary but can be triggered has a reaction to physical stress or Lunar Pressure (the force that compels werewolves to shift form into wolf form).