What is the “triumph” referred to in the following sequence of actions/lines?



Enter HAMLET behind, crossing the stage, reading a book – as he is about to disappear GUIL notices him.



GUIL [sharply]: Rosencrantz!

ROS [jumps]: What!



HAMLET goes. Triumph dawns on them, they smile.



GUIL: There! How was that!

ROS: Clever!

GUIL: Natural?

ROS: Instinctive.