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Beardie's do stretch their skin before they shed, so that is probably what he is doing. The picture honestly doesn't look like he is doing anything THAT weird. Well, in my opinion.
While that is exactly what you described, now that I see it, 'That' is not what I was visualizing when I read it & made my earlier comment. If that makes sense . And I got a kink in my neck watching it , to get the right orientation, lol.
Kidding aside ... That is strange behavior, almost looks like you said, that it was gagging or trying to regurgitate something. I haven't seen anything quite like it other than an actual puke. The good news is that you say that it seems to have passed or cleared whatever was causing it & that it is not an ongoing issue. Should this activity continue, I would have it checked, as it could mean a blockage of some kind, that it can't get clear on it's own, to be on the safe side. If it does not continue, he should be just fine, as he was able to get whatever was irritating it free & clear.
The orientation wasn't a biggy, was just my feeble attempt at a funny . But if you ever run into the issue again, it is important enough & you want to go to the trouble of changing it. If you are running Windows, Movie Maker that is in the free 'Windows Live Essentials' package from Microsoft, will allow you to correct it very easily.