The Epidemiologic Triad has been applied to the study of injury by scientists at the Centers for Disease Control and Prevention (CDC). For injury, the agent is any one of the five forms of physical energy: kinetic or mechanical energy, chemical energy, thermal energy, electricity, and radiation. This energy is conveyed to the host via a vector, such as a biting dog or snake, or its inanimate counterpart, the vehicle. Examples of potential injury vehicles are crashing automobiles and speeding bullets.