Scarlett O'Connor's breakdown in the later half of season 2. Her verbally abusive mother suddenly comes back into her life and gives her even more stress than she was already experiencing from the high demands of the tour. Finally, at one concert, she goes on-stage to perform and sees angry faces of her mother everywhere she looks in the audience. To further illustrate how nightmarish Scarlett's POV is, it's shot in blurry vision and a lower framerate, and the editing is far more rapid than usual for the show. It's appropriately unsettling.
