The student has to "speak" the piece very clearly. Therefore, he has to articulate more from the bow. The professor shows and clarifies the note groups of the phrasing. In this piece, dynamics move at the same time as the tempo.
There are also corrections on portato, sound control - when changing the string -, meaning of "ruhig" (calm) and technical work on double stops. The string change has to be anticipated by the fingers and each interval has its own character and expression. The expression is what sets us in motion and not the metronome.
The professor explains the rhythmical relation between 6 and 4 (sixteenth notes). He wants the student to clarify the changes from major to minor and, in general, to have a deeper connection within the phrase between the climax and either tessitura or character changes.
Finally, some comments on Hindemith's music and his value as a composer.