I don’t agree. It looks like an effect achieved through overlapping images, drawing from the same well as Dern’s distorted face in Inland Empire.
What
might have been done is that a slow-mo was shot, then computer manipulated further.
The normal speed for a movie is 24 frames per second. If you want a slowed down filmed shot, you have two choices. The first is that you shoot at a higher speed on set or location. That way, you run the film camera at 48 frames per second so that, when it plays back at normal 24fps, the image will be slowed down to half the speed. Shoot at 96fps and the shot will be a quarter of the speed in the movie. It creates a nice smooth slow-mo. However, that method uses up film stock quickly, as a quarter speed slow-mo shot uses four times as much film stock, which is pretty uneconomical.
The other easier option is to shoot at 24fps, then - in post-production - insert a duplicate of every frame, so each individual image runs for two frames instead of one. That will also slow down the motion, but makes it judder.
Both methods have their uses. John Woo, in his 80s and 90s classics, uses both methods for artistic effect.
The shot of Laura smiling looks like it could have been shot at a higher frame rate, but it's possible David Lynch slowed it down even more. In the digital age, when you slow down something that has already been shot, you can use computer software to scan all the original frames, then work out what a frame between those two frames might look like. It can take a bit of tweaking, but it's quite effective. It's a variant of the morphing effect used since at least The Abyss. When I'm working on corporate videos, for example, if an interviewee is sitting fairly still and there's a jump cut, because I've removed something he's said, I sometimes use a four-frame morph that can cover that jump cut.
So Laura's slow smile, which I believe is genuine, might have been slowed down even further than when it was shot. If it was shot at, say, 96fps, Lynch might have interpolated frames to give the impression it was shot at 192fps, for example.
Sorry if this is 'geek-speak'. I'm trying to keep it as simple as I can!
