I might be a little biased, but we look at each other to see what we are doing or to see if we are ready for the next step. Our conduct also lets each other know what we are thinking and we communicate this way silently with one another.
Among other things, we do not tuck our ties into our shirts between the spaces provided by spacing of our shirt buttons. Another such tradition was observed recently at the south lawn at the White House. It was silent and in all probability noticed; it was seen but not noticed. To us Marines, the message was ever so loudly expressed.
This tradition evolved from the days our Navy used riggings. The assigned Marine orderly (guard) to the ships always faced the ship's captain regardless whether the Marine orderly would end up facing the captain's front or back; regardless of the captain's direction of movement. The reason the Marine orderly always faced the captain was in order to be ready to receive an order.