Despite popular belief, the Queens Guard aren't purely ceremonial. While serving as the Queen's Guard they protect official royal residences, but they are also fully trained and operational soldiers.
The Queen's Guard's shift at their post lasts 2 hours. Every 10 minutes the sentry comes to attention and does a march of 15 paces across the area of the post. They also participate in the daily Changing of the Guard ceremony, which is when a new guard changes duty with the old guard. The guard may not eat, sleep, smoke, stand easy, sit or lie down during their tours of duty. To eliminate nuisance or suggestion of threat from members of the public, the guard will begin with "stamping" (coming to attention sharply). He will then shout: "Stand back from the guard." If this does not eliminate the threat he will repeat the stamp and shout. If the threat continues the sentry will point his rifle at the source of the interference with his duties. The guard then has the choice of detaining the person or pressing the button in his sentry box to summon the police.