Because most of the students have a couple of years of experience working within dramatic situations and know how dramas "work", the teacher does not spend much time setting this drama up. Perhaps, if the class was generally less experienced working within dramas, he may have chosen to attempt to describe what working in role means and how dramas "work". Of course, it is best for students, whatever their level of experience, to discover these things simply by "doing". Teachers should always remember that a drama can be stopped at any time in order for the class to discuss what is happening.