Saltonstall was a politician featured heavily in the game's 2010 gameplay demo but was cut during development. Despite this, he is referenced twice in the final game. First during the game's opening chapter where an NPC can be heard talking about him, and second in the chapter "Emporia" where a sign can be seen covered in scalps of prominent figures, including Saltonstall.

During the game's opening, the man who attempts to baptize Booker echos the phrase: "Is it someone new?" This is the same line spoken by the first splicer encountered in the original Bioshock.

Bioshock's series creator, Ken Levine, has stated that he hates seeing pornographic fan art of Elizabeth. In a Reddit AMA, he said that it's like coming across porn of your own daughter, and that he "die[s] a little inside with every page view."

In an early build of the game, the Barbershop Quartet in New Eden Square were called The "BEE" Sharps. In the final version, the band's name was replaced with "Albert Fink Presents." It's likely that the original name was a reference to The Simpsons, in which Homer was in a band called The Be Sharps.

Located in the audio data of Burial at Sea Ep. 2, there is a file called "sfx_evt_inf_alley_loop_01". While it sounds like nothing more than creepy ambient music, if reversed and sped up 150%, it's actually an altered clip of Spoiler:Sally being burned at the end of the first episode.

Some distant building models display an older Comstock graphic which does not reflect his final design. This suggests that these buildings come from earlier builds of the game, perhaps as far back as from 2010.

Elizabeth was originally going to be mute, because Irrational Games wasn't confident in their ability to create a talking companion character, and were worried that repetitive chatter or quips would annoy the player. However, they felt that having to focus the camera on her for her to communicate visually interrupted the player's experience too much, and was also annoying. They were faced with the decision to either cut her completely, or commit to making her a speaking character, and the decision was very controversial around the studio at the time.

The ambient rumbling noise that can be heard in some parts of the game is actually music that has been pitch shifted downwards. Audio director Pat Balthrop was surprised that people discovered this by playing recordings of the game at high speed.

There is an unused vendor that was going to be used as a tailor machine. All of them are destroyed in game, although a single piece of equipment can be found within each of them. However, they have cut subtitles that seem to hint they were once going to be usable in the game.

At the end of the game, Spoiler:while exploring the various lighthouses with Elizabeth, an unused snowy hill, observatory and bridge can be found far off in the distance, hidden under the game's map. The door to the observatory is functional, but only leads to an infinite void.

One of the available Voxaphone recordings in the game is of Spoiler:Fink talking about seeing a blueprint of a merger between machine and man. This suggests that Fink had seen a Big Daddy blueprint through a tear.

The Old Man Winter Plasmid used in the "Burial At Sea" DLC was created by Joe Trinder. He posted the design on the game's official forums. Trinder's design was immediately praised by other fans, quickly gaining attention on Reddit and even earning the approval of BioShock creator Ken Levine. Within a day, Irrational contacted Trinder and asked for permission to publish the poster on their Facebook page. A month later, the team bought the design from Trinder, and told him they planned to use it in the game. His initial version was for a Vigor, but it was changed into a plasmid to fit with the game's DLC.

Spoiler:While in Rapture, Booker uses the Bathyspheres for transport. According to an Audio Log in Bioshock, the Bathyspheres were locked to Andrew Ryan's genetic code, and because Jack, the protagonist from Bioshock, had similar DNA to Ryan, he was able to use them. This may imply that both Booker and Elizabeth are in some way related to Andrew Ryan.

When in front of the ticket salesman for the First Lady Airship, if you do nothing or demand the tickets, the salesman will stab you in the right hand, making Booker wear a bandage around that hand for the rest of the game. This is considered canon as this is how Booker is seen in all of his promotional art and even the front cover.

In the Warden's Office of Comstock House is a record player, with a record on it which reads "Rapture Records". This is a reference to the city of Rapture from the previous Bioshock games.

Spoiler:Right after Songbird dies in Rapture, if you look out the window you can see a little sister crying over a dead Big Daddy.

The propaganda poster featuring a little boy playing with toy soldiers and a little girl sitting on her father's lap asking him "Daddy, what did you do during the Siege of Columbia?" is based on a British World War I recruitment poster with the same illustration, but reads "Daddy, what did YOU do in the Great War?".

After a competition held by Irrational Games for fans to submit their names to be used as part of an in-game advertisement, the lead artists had picked entrant "Payton Lane Easter". The advertisement created which incorporated the name was "Payton Lane Easter & Sons Premium Automated Stallions".

In the Graveyard Shift Bar in Shanty town, if you head down to the cellar a guitar can be found. Elizabeth will state "I wish I could play" and if the player interacts with the guitar, Booker will start to play the guitar, and Elizabeth will sing along.

The letter Spoiler:old Elizabeth gives to young Elizabeth says:

"I am a code. I should probably be changed over for something much more official in the future. But I'll do as a stand-in for now I suppose."

The developers likely forgot to change it.
The cipher used for the letter can be seen early in the game in one of Elizabeth's many rooms.