The Shortest Horror Story I Could Think Of

A friend of mine emailed me a short-story writing challenge along with a few examples. The theme was short horror stories. 

The stories were supposed to be limited to two sentences, but I wasn't able to think of anything scary in two sentences that didn't seem derivative (i.e., "I tried to lay the large floral arrangement gently upon the casket, but in my grief I dropped them with a loud thump. Then I suddenly realized...the thump had come from inside the casket.") 

So, using 5 sentences, I came up with this:

"C'mon Duke, fetch the stick! Get the stick boy! That's a good doggie!" 

As Duke came running up the gently sloping hill I could see he had once again picked up a stick other than the one I had thrown for him. As he got closer I realized that it wasn't a stick at all...it was a human forearm, hand still intact, dripping fresh blood from the elbow joint where it had been torn off.

Duke trotted directly to me and dropped the arm. Looking up with a malicious gleam in his eyes he spoke, "I guess I'm not such a good doggie after all."