How old's the dog? The only explanation I can see for this other than "shock collar" is some kind of arthritis or other pain issue that when she stepped back up she had a little pain. Large breeds like her are prone to these issues and at fairly young ages in comparison.
However, a couple things - one, he apparently never uses this as an excuse. Two, if she had mobility/pain issues this means he hasn't gotten her diagnosed or treated her for it any way. Three, while it might just be her wrinkly face, she looks extremely fucking depressed in that clip. Four, regardless of whether she is or isn't depressed, she was absolutely uncomfortable and nervous beyond all doubt.
Why does he have a large dog laying down in one spot all day long when it clearly does not want to be there? Don't people watch animals to see them, you know, doing something? Like people who go to zoos and tap on the glass or throw things into enclosures. If the whole point of this animal was for something to entice viewers, wouldn't he WANT her to be moving, playing, wandering around and such? And if he wanted a supermodel dog to just lay there and be pretty, why didn't he just get a lazy ass potato brained dog who would be happy to snooze 8 hours a day?
But let's just ignore all of this. Why the fuck is he using a shock collar? Shock collars do have a use and are good tools if the dog does not respond to other teaching methods (this absolutely happens, don't listen to the nuts who tell you every single dog ever born is an obedient sweet baby angel who follows subtle social cues), if it has an extremely high instinct drive to the extent it ignores all other input when focused, or if the behavior you're trying to curb is dangerous and needs IMMEDIATE feedback to protect them. This dog looks laid back as hell and shouldn't need more than a vocal or hand gesture correction to make it go back to its bed. Even if a shock collar was needed for her to listen at first (which I doubt), she does this all day every day? She knows the drill. She doesn't need to be shocked, she'll obey your command even if it's only because of fear. He then tries to cover up his use of a shock collar by making fun of his dog? My dog has joint problems and occasionally will yelp when getting up and I ALWAYS get up to check on her because the sound is distressing and even though I know what it is I want to make sure she's okay and comforted. Abdolutely psychopathic behavior all around.