>>648170335It looks like its just 2 frames. They hold long enough that you can keep your eye on the right side of the image, looking for the big red part of the train. On one frame it's kind of in the middle of the image and in the other frame it's far to the right. By switching your gaze between those locations in time with the frames to keep looking at the red part it looks like it's going back and forth rapidly.
