This is a shot of Danny hiding in the metal pantry later on in the movie. He is screaming the moment Jack kills Halorann, but currently we are watching it as part of Danny's vision from Tony while in the bathroom. Contrast Danny's extreme reaction to his first encounter with the hotel against JACK'S nonchalant response. Danny understands the hotel through and because of his duel personality, he only received this vision because he begged Tony to give it to him. Danny allows himself complete awareness (Tony is the 'nonchalant' one) and therefore extreme shock at the truth of the hotel.