Visible crew/equipment: When Monica is in bed with her boyfriend and they get up to dance, the whole film crew is mirrored on the glass of the window.
Revealing mistake: At the party someone asks Marcus his name and he replies 'Vincent' the actor's real name (Vincent Cassel).
Chosen answer: The flashing lights are to create a sense of uneasiness again. Gaspar Noe uses low frequency sound to create nausea, headaches, and disorientation in the beginning and uses it again here to make the viewer feel sick after the mood changes dramatically. Also it symbolizes the chaos that occurs in the universe & how life can easily spiral out of control as it does in the movie.
Dra9onBorn117