This video shows canisters of laughing gas left on the floor of a London Underground train following Notting Hill carnival festivities on August 27.

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.

Amid the festivities, local media reported that over 200 arrests were made as police uncovered knives and other offensive weapons.