This video shows canisters of laughing gas left on the floor of a London Underground train following Notting Hill carnival festivities on August 27.<br /><br />The carnival, attended by an estimated one million people, took place on Sunday and the bank holiday Monday. Revelers enjoyed parades, float displays and performances at the annual event.<br /><br />Amid the festivities, local media reported that over 200 arrests were made as police uncovered knives and other offensive weapons.
