Just like most things on the internet, the subreddit Don't Dead Open Inside wasn’t created out of nowhere. The trope first came to internet users' attention when its name was used in a promotional poster for the TV series The Walking Dead. To this day, the Don't Dead Open Inside poster, revealed on July 2nd, 2010, stands as one of the most recognized examples of the trope in popular culture that caused the cult following on Reddit.

According to Know Your Meme, the infamous poster featured a photograph of a double door with the words "Don't Open" written on the left side and "Dead Inside" written on the right, which should be interpreted "Don't open, dead inside" if read in the correct order. The whole fun of the trope is revealed when the reader reads the phrase line by line instead, which sounds like "Don't dead open inside."

Knowing the speed things surf around social media, it shouldn’t come as a surprise that a couple of users on Twitter shared their reactions to the unusual poster on social media. In the following years, “the memes based on the joke were made, with Know Your Meme user irish_swede archiving one such example on March 12, 2013,” reported Know Your Meme.

On May 17th, 2014, the subreddit r/dontdeadopeninside was created, where the community collected cases of the trope found in popular culture, design, advertising, etc. Today, it’s home to 603k members that follow a strict set of rules for submissions.

The first and most important rule is that all posts have to comply to DDOI format. “Signs must be read correctly top to bottom, and incorrectly left to right, like any text, usually. Though it does not matter how easily you can read them, it is highly encouraged to only post images with little separation or spacing between the columns of words.”

The community doesn’t allow both reposts and memes, and encourages users to “put the 'correctly read' way in the title, like 'DONT DEAD OPEN INSIDE.'”