Don Hertzfeldt/Nightmare Fuel


 * The robot that looks like a smiling mouth.
 * The hallucination scene from everything will be ok, mainly the parts where the entire screen is covered by flashing lights and shapes, along with what looks like a blurry, deformed pig's head flapping its jaws in the foreground. All the while the music becomes more frantic and jarring until it's basically nothing but static and noise.
 * Wisdom Teeth is both this and Nausea Fuel, especially as the short reaches the (literal) end of its thread. If you have issues with teeth and dental issues, this is not the cartoon for you.