Some variant games also exist. Double box involves a short rectangular field with two small end zones rather than one; there is no clearing line, but when a team gains possession of the disc after a turnover they must attack the end zone that their opponents were not. A variant originated in Washington, DC, Boot-Box, combines Double box with the cone hitting game, Durango Boot. Two end zones are formed with a square of four cones. Before scoring a team must complete a pass across a mid line. They can then score at either end zone. One point is scored for each cone knocked over. Catching a disc and landing in an end zone scores 3 points. Games are played to 15. Invalidimate was developed in the UK as a way to include injured players in practice; the "invalid" stands in the goal and is the target receiver for both teams. Two invalids can also be used in double box, with the additional rule that every player on a team must touch the disc (including the defensive invalid) before the offensive invalid can catch a scoring throw.