It does take much to make a good scary story. You can design short stories to evoke fear in only 150 characters or less. With the creative use of imagery and inference, you can tactfully lead your reader to a fright or a giggle with minimal wording. Good writing can prey upon old beliefs and prior knowledge. You can use this information to formulate two sentence horror stories that tell just enough (and leave just enough out) to complete your objective.
Here is One Scary Tweet: