You enter a clearing, he moves like a bird lightly bobbing his head; and you keep still because you think maybe his visual acuity is based on movement like a T-Rex. He'll loose you if you don't move. But no, not Dr. Alan Grant.
With this shirt he knows your a member of his dig crew in Snake Water, and now he sees you showing up late. You stare at him and he just stares right back.
Next time maybe don't celebrate the new find so late at the bar, and ya'know... try to show a little respect.