Injuries to the skin are traditionally divided into two categories: those caused by sharp forces and those caused by blunt forces. Sharp force injuries are those that occur from objects having a sharp edge or point like a knife, axe, or piece of glass that incise or cut into or through the skin. Abrasions are also caused by blunt force trauma but occur when the force is applied in a scraping or abrasive action that results in removal of part or all of the skin's outer layers. Impressions made by footwear on skin are typically encountered in violent crimes when the perpetrator kicks or stomps on the victim. They are also encountered when the victim has been hit with another patterned object, or run over by a vehicle. The forensic examination of a blunt force footwear pattern injury with known footwear requires the same knowledge, training, and procedures used in any other footwear comparison.