The film's director and effects team had one goal — to make their Oklahoma tornadoes look as real as possible.

As the first step, animators made a set of controls so they could basically animate big sculptural shapes of tornadoes around the landscape. Then we'd work out the choreography, and then the ...

The tornado ... you see this big funnel cloud touching down,” said Collin Morrissey, a guide for SeaDaddys Dive Center. “[I] thought it was water spout. It was kind of scary.