The set-piece where the F5 tornado begins hurling farm machinery into Jo and Bill's path was achieved by suspending the equipment from powerful helicopters and then releasing them on cue. The red pickup was then driven through the wreckage as it hit the ground and CGI was used to add debris including the steel wheel that bounces in front of the camera. The collision of the truck's window with one of the parts of the harvester is real and was not intended, hence the continuity error where it appears intact in the following shots.