Solomon isn't an easily startled person. He isn't visibly startled either. But sporadically throughout the movie, his fingers would tighten on Sam's arm - he's not entirely sure when he grabbed her arm, but it's in his fingers now. That's the only reaction he has to the movie. It doesn't show on his face, or anything else, just those minutely, sporadic tightening fingers. Once whatever tension is on screen ends, his fingers loosen, but he never fully releases Sam's arm for the rest of the movie.