It Happened One Night.

Wait, did it? What happened? Which night?

The most likely answer is that two strangers randomly met on a bus one night and started an unexpected adventure that would bring them together.

But maybe "what happened" is that they fell in love, and it happened "one night" in a barn over a dinner of raw carrots.

Or maybe what happened was sex, and it happened on the last night shown in the film.

Who knows? That's part of the fun: The title of the film is as quirky and mischievous as everything else about it.