This process is termed aspirating the needle or registering. When accessing a vein with unobstructed blood flow, a "flashback"—or sudden flash of red blood inside the needle tip—may occur spontaneously when the needle enters the vein. Because sudden appearance of blood in the needle/syringe alone does not guarantee proper needle placement (flashbacks can also occur when a needle passes through a vein completely, enters an artery inadvertently, or otherwise is extravasated), aspirating the plunger on the syringe is still considered a requisite step.[14]