The last man on Earth sat alone in a room. There was a knock on the door.
A story could be 'I woke up. My reflection blinked first.' It's short but gives a spooky feeling as it makes you question the normality of your own reflection.
It might be something like 'The last man on Earth sat alone in a room. There was a knock on the door.' This is super scary because if he is the last man, who could be knocking?
One possible interpretation could be that it refers to a horror story that is extremely concise in terms of length. Maybe it's just a few words that manage to convey a truly terrifying concept, like 'The last man on Earth sat alone in a room. There was a knock on the door.' It leaves a lot to the imagination and creates horror through the unknown and the sense of impending danger.
One possible theme is the brevity of love. Just like in the short story forms, it shows that love can happen and end quickly.
Themes in the 'world's shortest short story' can include love in a very distilled form. Maybe it's just a single word or phrase that implies a deep love. Also, death can be a theme, perhaps shown by a simple reference to the end of something or someone. It's all about packing a big theme into a tiny space.
One could be 'The last man on Earth sat alone in a room. There was a knock on the door.' It's short but extremely creepy as it makes you wonder what could be knocking when there's supposedly no one else left.
One interpretation could be that it represents the simplicity of the act of going to sleep. For example, 'Bed. Sleep.' It's like stripping away all the fluff and just getting to the basic idea.
Another way to look at it is that these short horror stories play on our primal fears. Consider 'The mirror showed no reflection.' Mirrors are often associated with self - identity, and not seeing a reflection is against our normal experience, which makes it very scary. It could symbolize a loss of self or the presence of something supernatural that blocks the reflection.
One possible interpretation could be a story that quickly creates a sense of dread. For example, 'The last man on Earth sat alone in a room. There was a knock on the door.' It makes you wonder what could be outside the door in a world where there should be no one else. It plays on our fear of the unknown.
I think 'Looked in the mirror. Saw someone else.' qualifies as one of the shortest. It gives that sudden shock in a brief sentence.
One interpretation could be that it creates a sense of dread in a very concise way. For example, if the story is just 'The last man on Earth sat alone in a room. There was a knock on the door.' It makes you wonder who or what could be knocking when there's supposedly no one else left. It plays on our fear of the unknown and isolation.