The Scene: At the end of the movie, Céline (dith Scob) drives the limousine to the Holy Motors garage, and after she leaves, the limos start talking to each other, whining about their clients and expressing fear that they may become obsolete soon enough. Sure, it's hard to make sense of most of the movie, but this one really takes the cake.
What It Probably Means: The movie as a whole has been recognised as a critique of the modern film industry, and the limousines throughout the film can be seen as the literal and figurative "vehicle" which allows Mr. Oscar (Denis Lavant) to give his performances across the city. A crucial line comes at the end of the limo discussion, when one says, "Men dont want visible machines anymore", and within the scope of cinema, it's hard not to interpret that as a slam against digital filmmaking, which is of course known for its smaller technology with greater accessibility. The limos are, by contrast, the titular "holy motors", cherished, classic relics of a time mostly bygone (of shooting on film).
Or maybe it all means nothing and director Leos Carax was just seeing how much crap he could get film critics to write about something which makes no sense.
Which movie scenes do you find the most confusing? Shout it out in the comments!