A vent is usually a medium sized hole in the wall used for air circulation. In most games, they're used for getting from one room to an other. The character usually crawls through them. When the character gets into a vent, the camera often switches to first person because of the cramped nature of the vent tunnel. While vent crawling, the player can alert enemies of his or her presence because of the noise that is made while crawling through the vent. While vent crawling, the player can spy on enemies and even drop on an unsuspecting enemy. Vent crawling can also be an easy way to escape enemies or sticky situations.