The Held Frame Is the Thumbnail
The clip is the motion. The share is the still.
Two things, one clip: a World Stop video is two scenes - before and after - with a single held frame between them. The held frame is where the transformation is not yet visible but the motion has stopped. That frame is the moment of maximum tension, and it is the one the platform cuts into the thumbnail automatically.
Why people screenshot it: the held frame is a still image of a moving person. The hair is frozen mid-flip, the arm is frozen mid-swing. It is a single moment that could not exist outside of that exact clip, and that is what makes it the one image people save and send. The clip is the event. The frame is the souvenir.
The game plays the hinge: in the World Stop remix, you do not watch a transition, you create one. A scene is in motion, you tap to freeze it on the beat, and then you choose which transformation lands in the held frame. The card is your freeze timing and your best frame.