"Are you rushing, or are you dragging?" is the violently unveiled threat posed by J.K Simmons' Terence Fletcher moments after striking his faltering student in a sudden, unpredictable act of brutality that sets the electrifying tone for Whiplash, a flawlessly paced film which is never guilty of either offence.
The impossibly-paced beat that Fletcher demands of his student is mirrored in Simmons' ability to register intense psychological changes in the blink of an eye. A gentle criticism becomes a vitriolic threat in less than a beat; a tightening of his lips can devastate or elate his musicians, and has no less compelling an effect on the audience. Fletcher quite literally snatches the music from the air with a sudden tightening of his fist, indicative of the incredible control practised in all elements of this film.
Director Damien Chazelle's control in no way limits the film's emotional reach, however. Miles Teller batters against the airtight structure of the film, delivering an incredible performance as Neiman spirals into a sadomasochistic deadlock with the ambiguously antagonistic Fletcher. We get the feeling that we can never quite figure each character out, that they never pause long enough for us to understand them; Neiman is endearingly awkward and then callously single-minded; Fletcher is impenetrably cruel and openly but fleetingly vulnerable in his inscrutable grief over a former student's death.
Their psychologically-charged struggle climaxes in the breathtaking final act, in which we are never allowed to rest in one emotion for more than a beat and the utterly unpredictable finale delivers its punches at a breakneck pace. It is in the communion of the final scene that the nature of the film is properly exposed; jazz is Chazelle's vehicle rather than his focus in this dissection of the nature and the physical demands of genius, imbuing it with the pulse and climax of the music to which it is set.