Smile Dog is a creepypasta centered on an image called "smile.jpg." Anyone who sees the photograph of a dog seeming to grin like a human is said to suffer terrible nightmares and hallucinations from that day on, a torment that stops only if they spread the image to someone else. "Spread the word" is the command of this curse.
The heart of the horror is the compulsion to propagate. Because the only way to end the curse is to pass it to another, the victim becomes the perpetrator. The structure in which the act of seeing becomes infection and a record spreads itself is a prototype of memetic horror, where information itself is the threat.