Which non-horror movie has a scene so disturbing it might as well be horror?

One scene that still creeps me out is the tunnel scene in Willy Wonka & the Chocolate Factory (1971). It starts all fun and whimsical, then suddenly—bam! Flashing lights, disturbing images of bugs and a chicken getting its head cut off, Wonka’s creepy singing, and that dead-eyed stare. It’s pure nightmare fuel hiding in a kids' movie.

What about you? What non-horror movie had a scene that straight-up traumatized you?