Rodriguez is known for his technical experimentation, and Spy Kids is one of several films he's directed in 3D. In fact, this film is advertised as a 4D release, with the extra dimension provided by a process billed as Aroma-Scope. This feature requires a scratch 'n' sniff card, featuring eight scents intended to complement the viewing experience. Unfortunately, most of the smells are indistinguishable, and scratching the card is a distraction from the film. Nevertheless, the concept is introduced by Ricky Gervais, in a hilarious voice-over cameo role, at the start of the film. (The film is also showing in 2D with Aroma-Scope.)
It's a gimmick, of course, inspired by the Odorama cards John Waters produced for his bad-taste comedy, Polyester. The first experiments with scented cinema occurred fifty years ago, when smells were wafted through cinema air-conditioning vents to accompany the documentary Behind The Great Wall (via the Aroma-Rama process) and piped to cinema seats during the thriller Scent Of Mystery (using the rival Smell-O-Vision system). Like Cinerama and 3D, they were Hollywood's attempts to lure audiences away from television.