Relying on a low budget of $50K, the movie was shot over five nights in a single location with dialogue that was largely improvised.
The actor who plays Amir, Alex Manugian, is also the co-writer. He was essentially "the mole" who helped guide scenes if the actors went astray.
When Kevin (Maury Sterling) tries to leave the house by himself, Em (Emily Baldoni) was given a note to not let him leave and his note was to leave.
Instead of scripts, the actors would each receive only a small paragraph (that only they would see) as their 'goals' for the day. This allowed for the story to unfold naturally and create genuine reactions in the other actors.
The set only had 5 crew members: 2 sound guys, the director of photography, the director, and producer Lene Bausager.
Emily Baldoni wanted to immediately bust the box open when it was first discovered. The director, James Ward Byrkit, had to step in since the filmmakers only had one box.
Three rental cars were used for the breaking of the glass. The windows were replaced before the cars were returned.
The director, James Ward Byrkit, wanted to use his own house as the setting of the movie. Since his wife was 8-and-a-half months pregnant and wanted a homebirth, she agreed to let him so long as he could do it in 5 days.
The story took a year to write.
According to Emily Baldoni, after the first mysterious thumping on the "door to nowhere", the actors were both scared and very excited about the story that was unfolding. "Of course we knew we were in good hands, but this is when things got really exciting, because we could see how genius and well-planned everything was. We just didn't have any clue."
Lorene Scafaria (Lee) had the least idea of what movie was being filmed since the rest of the cast had done test footage before. She only knew it was going to be improvised. About the third day of filming, she realized it wasn't supposed to be a big, broad comedy.
The neighborhood was supposed to look completely dark when the first group visits the other house. It was the same night a Snickers commercial was being filmed in the neighborhood which used huge lights and hundreds of people.
The director, James Ward Byrkit, said the hardest part of directing was keeping everyone quiet since there were so many people who were compelled to speak a lot.
There were only two cameras used throughout the filming of the movie except during the dinner scene which had one additional camera.
The reason the cameras are so shaky was not so much a stylistic choice as it was giving the actors the freedom to go anywhere they wished to.
The filmmakers do not reveal how the comet was filmed other than to say it was a practical effect.
Both sides of the phone call at the beginning of the movie were recorded together, instead of the more common practice of adding in the other side later.
The idea for the story came from wanting to tell a story that takes place only in one room.
Maury Sterling was terrified about improvising.
The director, James Ward Byrkit, first met Lauren Maher (Laurie) while working on Pirates of the Caribbean: The Curse of the Black Pearl (2003). She played Scarlett, the wench who slaps Johnny Depp.
Test footage was filmed a year prior. The role of Mike's wife (played by Lorene Scafaria) was originally played by the director's wife. She chose not to be in the final film due to being 8-and-a-half months pregnant.
Some scenes were reshot six months later. Lorene Scafaria (Lee) changed her hair during this time, so they spent $8,000 getting a wig that matched her original hair. This was as much budget as the entire first shoot.
Elizabeth Gracen and Lauren Maher, while enemies in the movie, are great friends in real life.
Lorene Scafaria (Lee) was just finishing writing/directing Seeking a Friend for the End of the World (2012) before filming.
Hugo Armstrong (Hugh) was the one to actually break the car windows.
Emily Baldoni's hair at the end of the movie took a long time to appear messed up after sleeping, because it kept falling back into place.
The producer, Lene Bausager, flew out from England specifically to make sure the movie would happen.
Alex Manugian (Amir) & Lorene Scafaria (Lee) waited for 2hrs in 40 degree weather before the dinner scene awaiting their entrance. They huddled around the hot dinner they were bringing for warmth.
Emily Baldoni (Em) figured she was the lead of the film around the time that it's shown that she figures out what the numbers mean.
The car that Em (Emily Baldoni) knocks out her doppelganger in is her car in real life.
The flickering lights in the bathroom at the end are not an effect but actually an assistant turning the lights on and off.
When the original Amir (Alex Manugian) & Hugh (Hugo Armstrong) finally return to the house, there was a 45min standoff from the others in the house who wouldn't let them in. The director had to step in and allow them in so that the story could progress.
When Em (Emily Baldoni) leaves to find a new house, a deleted scene had her pass one where a seance is held over the dead body of Mike (Nicholas Brendon).
Emily Baldoni & director James Ward Byrkit's favorite scene is when Em (Emily Baldoni) meets "other" Kevin (Maury Sterling) after checking on the car.
The night Em (Emily Baldoni) went searching for different houses was filmed was the same night the director's wife had their baby. It was homebirth held in the same house the movie was filmed in.
There is a deleted scene that explains that the photo of Amir (Alex Manugian) is printed from a battery powered printer of Kevin's (Maury Sterling) due to his profession as a photographer.
(at around 32 mins) The director, James Ward Byrkit, says his favorite line is said by Alex Manugian (Amir): "We're not splitting up; we're just going into groups." Ward describes it as the skeleton key to the whole movie and also speaks to the subversion of movie tropes in the movie.
The debate about what's happening shortly after the book is brought in went on for 45mins and included a speech from Kevin (Maury Sterling) where he talks about traveling through the Middle East.
(at around 1h 6 mins) When Hugh is calculating the different outcomes on his iPhone, the number of different outcomes is 5,038,848 = (6^8)*3 meaning 6 numbers per person, with 8 people and 3 glow stick colors per house (though the usability of colors in the calculation is questionable).
The blackout cuts used as scene transitions are strategically placed. The filmmakers have implied it has something to do with the fracturing of realities and fit certain rules. Act 1 ends with Kevin (Maury Sterling) discovering the duplicate note, but the blackout cut is not used to transition into the beginning of Act 2, because it does not fit the rules.
In the beginning of the movie, Mike (Nicholas Brendon) says that he played a character on the TV show Roswell (1999-2002). This may be a reference to Brendon's real role on Buffy the Vampire Slayer (1996-2003). It could be an early hint, showing a different reality, in which he played a different character on a different 90s teen series.