The process of creating the scene was painstaking, over and over again one actor would sing a line, move and gesture while the other observed him. Then the second actor would sing his line and move and gesture in the same way. They were free to work out what felt right for the characters, but restricted to what the character required. Within the bounds of the specific character and the interpretation of the play by the director the students are asked to try various gestures, postures and ways of expressing the lines. The director may ask what they feel is best for the part or may ask them to analyze the motivation of the character.
Every character wants something from the other characters.
Those people who are not performers of some kind do not often sing out loud in public. Despite what musicals would have us believe, after childhood it is not really done to walk through a store singing a song. But in the theatre you can sing out loud if the feeling moves you. It is a very freeing and scary experience to suddenly burst into song. But in this scenario the words and music are already written and you must follow them.