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. She was stuck for 3 minutes before the stunt coordinator finally realized that something was wrong after he noticed that her handcuffs were stuck.
The card trick in the opening sequence works in real life too, there is no editing, contrary to popular belief. It is done by performing what is known as a "card force", wherein the magician makes the unsuspecting audience member pick a predetermined card. The audience member believes he picks a random card; a belief which is strengthened by the magician usually re-shuffling the deck several times. This is of course just misdirection.
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 Harrelson and Eisenberg had starred in, Zombieland.
Demonstrating that he really had learned how to throw cards with forceful accuracy, Dave Franco sliced a half of a banana into a further half with his hotel key card, while promoting the film on the Bob Rivers radio show (KJR-FM, Seattle).
After The 4 Horsemen get arrested, Merrit McKinley (Woody Harrelson) tells the FBI agent there's no shame for a man to wear a dress. This is a reference to J. Edgar Hoover, the long time director of the FBI, who was revealed to be a cross dresser after his death.
The license plates on the confiscated BMW were TNQ 8930. These same plates end up on Morgan Freeman's Land Rover AFTER it was shown to have different plates a few minutes earlier. They go go great lengths to make sure you can read theses plates. Something is going on here.
Both director Louis Leterrier and star Mark Ruffalo were involved with the Incredible Hulk. Leterrier directed _The Incredible Hulk_ (2008) and Mark Ruffalo portrayed Bruce Banner/Hulk in the Avengers films.
While in New Orleans, French INTERPOL agent, Alma Dray, is wearing a striped shirt. This is a reference to a famous French New Wave film, Breathless, in which the main female character, Patricia Franchini, wears striped clothes throughout the film. This look, along with short hair, became the "look" throughout the 60's and 70's. This "look" has been revamped among celebrities recently, as the popular culture looks to French New Wave as a retro and stylish inspiration.
When Thaddeus is telling Dylan on how the tricks on the first magic show was done, there is a flash back when the bank owner walks down the stairs in Paris and you can see some graffiti that reads "Taken". The movie Taken (2008), staring Liam Neeson, was based in Paris.
The trivia items below may give away important plot points.
During the interrogation scene, Merritt says that Dylan Rhodes has "big daddy issues." Later in the movie, proving Merritt's skill as a Mentalist, it is revealed that Agent Rhodes is the son of Lionel Shrike.
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 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 son's apartment.
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.
When the Horsemen enter Times Square, eyes flicker in and out of visibility in the billboards around them. The last to appear is the same Eye that appears on the merged tarot cards in the park, which lingers long enough to be seen clearly almost in the center of the screen.