Isla Fisher got into difficulty while filming the piranha tank scene. The top of the tank remained opened so that Fisher would be able to swim to the top to get some air, and there was also an emergency lever inside the tank that, if pulled, would alert the crew that she needed help. During one take, Fisher was running out of air and tried to swim to the top, but the chains on the handcuffs she was wearing got stuck on the bottom of the tank, so she was unable to swim to the top or pull the lever. She then attempted to alert the crew by hitting the glass of the tank, but since her character is supposed to be panicked and scared in the scene, the crew thought she was acting. The stunt coordinator finally realized that something was wrong after he noticed that her handcuffs were stuck.
In the scene before J. Daniel Atlas and Merritt McKinney enter the secret room, McKinney tells Atlas that he is a "bit of a control freak," to which Atlas replies "Have we met before?" This is a nod to the previous film, Zombieland that Harrelson and Eisenberg have done together.
When Jack and Dylan land in the garbage, above the Shrike magician prop box is an apartment mailbox labeled "Shrike" This is for apartment 6.A. and is the apartment of the four horsemen, previously owned by Lionel Shrike and later more importantly his sons apartment.
The trivia items below may give away important plot points.
Each of the tarot cards refers to a Horseman. J. Daniel Atlas' (Jesse Eisenberg) card is the "Lovers", referencing his implied sexual prowess. Merritt McKinney's (Woody Harrelson) card is the "Hermit", referencing how his brother abandons him and destroys his career, leaving him alone and with nothing. Henley Reeves' (Isla Fisher) card is the "Temple Priestess", referencing her trick with the bloody tank, similar to a blood sacrifice. Jack Wilder's (Dave Franco) card is "Death", and his is the only card with a meaning that is not explained until late in the movie, where he fakes his own death. The Death card in Tarot mainly means change, most likely referencing Wilder's change from being seen as a kid at the start to an actual adult at the end.
When Alma Dray is reading the newspaper in Paris, she reads an old article about Lionel Shrike's death happening in the 70s. Shrike can be seen in a front-page photo of the article. Shrike, in footage news, is played by Elias Koteas.