Spotting deepfake video in a short clip
Edges, blinks, and the mouth are the checks that survive when you only have a few seconds.
Pause is allowed. A clip that only works when it is moving fast is asking you not to look.
Scrub to the jaw and the hairline. A face swap has to repaint that boundary on every frame, and it often leaves a soft seam or a flicker when the head turns. Glasses and earrings make the seam easier to see because they are thin and they should stay attached.
Then watch a blink from start to finish. The lids should meet, and the two eyes should mostly agree. A blink that starts and then fades without closing is a classic artifact. So is a face that never blinks across a long sentence.
If there is audio, mute it for one pass and watch the mouth shapes. Then play the sound. Consonants need a closure. A mouth that stays in a talking oval while the words change is not speech, it is a texture.
The video quiz keeps the clips short for that reason. You get the explanation after you commit, including when the useful tell was temporal rather than something you could see in a screenshot.