<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> <P> The mat is usually replaced twice per year: before Memorial Day and before Veterans Day . This is required because of the wear on the rubber mat by the special shoes worn by tomb guards . The sentinels have metal plates built into the soles and inner parts of their shoes to allow for a more rugged sole and to give the signature click of the heel during maneuvers . The sentinels wear sunglasses because of the bright reflection from the marble surrounding the Tomb and the Memorial Amphitheater . </P>

Bodies in the tomb of the unknown soldier