 The documentary  _Great Movie Stunts: Raiders of the Lost Ark (1981)_ (qv)  inadvertently gives away one of the secrets behind the stunt where  Indy goes under the moving truck. The camera slate (visible in the  documentary) shows the camera was set at 20 frames per second  instead of the traditional 24 fps; in other words, the shots were  done in "fast motion," so the truck was not really moving as fast as  depicted on screen.