Horrifying things are scary and disturbing. A car crash, a violent scene in a movie, and an exposé on what's really in your fast food hamburger can all be described as horrifying.
Something that scares you to death, like the sound of footsteps upstairs in your dark, empty house or the sight of a bear on the hiking trail, is horrifying. Equally horrifying are things that sicken you, like photographs from a battlefield or the description of a painful dental procedure. Horrifying things inspire horror, originally a Latin word meaning both "dread" and "religious awe," from horrere, "to bristle with fear."