<Li> Repeats the routine until the soldier is relieved of duty at the Changing of the Guard . </Li> <P> After each turn, the Guard executes a sharp "shoulder - arms" movement to place the weapon on the shoulder closest to the visitors to signify that the Guard stands between the Tomb and any possible threat . </P> <P> Out of respect for the interred, the sentinels command silence at the tombs . If the guard walking the mat must vocally confront a disturbance from spectators, or a threat, the routine is interrupted, and remains so until the disturbance is under control . The sentinel will exit the mat, place the weapon in port arms position, and confront the disturbance . Once under control, the sentinel then walks on the pavement to the other side of the mat, turns to shoulder arms, and continues the routine . </P> <P> Twenty - one was chosen because it symbolizes the highest military honor that can be bestowed--the 21 - gun salute . </P>

How many guards at the tomb of the unknown soldier
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