Continuity mistake: In the bar scene, Alan gets soaked by Charlie's drink, covering his face, shirt, tie, and coat. But when Alex leaves he is completely dry and all the wet patches have just disappeared.
Trivia: The fact that the character of Charlie is shown playing the video game "Shadow of the Colossus" was an intentional choice by the filmmakers, who had to get permission from the game's director to include it into the film. It was decided Charlie would play this game based on the symbolism of the gameplay (which involves the destruction of giant "colossi", whose deaths are somewhat similar to the collapse of the twin towers during 9/11, and the fact that the main character is trying to bring someone back from the dead), and how it related to his character .
Trivia: Tom Cruise and Javier Bardem were originally cast as Charlie and Alan, but filming was delayed. Cruise dropped out and Bardem suggested Sandler for the role of Charlie, being impressed with his dramatic performance in the film "Punch Drunk Love." Eventually, Bardem ended up having to drop out due to scheduling conflicts and was replaced with Don Cheadle.