Generally, and at Oxford during Eights Week, once a bump has occurred both crews pull over to the river bank and take no further part in that race. At Oxford during Torpids a bumping crew pulls over but the bumped crew must continue racing over the entire course and can be bumped by more than one crew per day. As bumps racing usually takes place on narrow stretches of water, when contact occurs, two or more boats can become tangled up or not clear the river quickly enough, causing the racing line to be blocked. This can be very dangerous and the chance of boats getting damaged is high. To avoid this, the cox of the boat being bumped can concede as soon as slight physical contact occurs or even once it is inevitable. Nonetheless, collisions involving several boats are common. Crews in Torpids tend to concede bumps early to avoid being entangled with the crew that caught them: should they be unable to continue, other boats may row past, overtake and 'bump' the stationary crew. Any crew that has been bumped starts the next race behind the boat or boats that caught it; they switch places. A boat which reaches the finish line without either bumping or being bumped is said to have 'rowed over' and stays in the same position.