“Sometimes we’ll start on a trailer before they’ve even started filming,” Gritton says. “We just break down the script. Then we’ll get dailies—literally everything they’ve shot, hours and hours.” The dailies are covered in ghostly watermarks and stamped with the producer’s and house’s name for security’s sake, making them nearly unwatchable and of no real use to pirates. Theoretically.
Given the extraordinary and time-consuming process of CGI, sometimes green screens, motion capture dots on actor’s faces, maybe a cardboard cutout where a dragon will eventually go are still visible in these early cuts. “We’ll pick what we think are the best takes,” Gritton says. “The majority of the time it’s not what ends up in the film, which is why you see stuff in the trailer that you may not recognize later.”
As a recent example of this, there are several trailers for Baby Driver where we hear Doc describe Baby as "Young Mozart in a go-kart," [1] but this line is never heard spoken in the film (though we do see it written on one of Baby's cassette tapes).