The recent addition to the "Spy Kids" franchise is "Spy Kids: All the Time in the World". It's also billed as a "4D" film, meaning it is not only available in theatres in 3-D, but it also has another dimension of effects. To experience this effect, viewers need to use a set of cards at appropriate times during the film.
This effect is not new to films - variants of this have been tried as far back as the 1960s. But this has never really taken off and has remained an unnecessary innovation at best.
What effect is this?
Image: Wikipedia