This post was published more than a few years ago (on 2012-08-27) and may contain inaccurate technical information, outmoded thoughts, or cringe takes. Proceed at your own risk.
In the course of transferring film (24, or for our purposes, 23.976fps) to NTSC (29.97fps or 59.94 interlaced fields per second), we get what’s referred to as 3:2 Pulldown. What happens is that we get three fields from one frame of the film, two fields from the next, and repeat this forever. So, for frames ABCD of film, we get AA AB BC CC DD of video.