The game's original full title was Bioshock 2: Sea of Dreams.
Contributed by Boyobmas
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There is an unused video in the game's files called "gul_sinc_dies.bik" The video is low quality, silent and looping, implying it was originally meant to played on a monitor in-game. The video shows Sinclair bound to a chair, the title implies he dies soon after. Spoiler:In the final game, Sinclair is transformed into an Alpha Series Big Daddy and dies by your hand. The title also uses the prefix "gul". Oddly, the only other videos with the "gul" prefix are the cutscenes used for the end of the game.
Contributed by Boyobmas
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A frozen cat named Schrödinger can be found in Imago Fine Arts at the Dionysus Park level. This is a reference to the famous thought experiment Schrödinger's Cat.
Contributed by DeerBoarDude
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There is a Little Sister in Ryan's Amusements that is able to take damage and die. This is the only one of its kind in the game that is able to be killed. It goes into a T-pose after death with full physics, allowing you to hit the model afterwards.
Contributed by SOGESNAKE