Barium sulfide, if I remember correctly. It's a metallic compound able to show up on x-rays to check for abnormalities in swallowing.
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Edit: sorry @superbee, see you've also explained it!
Barium. That’s a video esophagram looking for dysphasia, or a swallowing disorder. If any liquid (barium) goes into the lungs, even trace amounts, it can lead to aspiration pneumonia. In the sick or elderly it can be serious; like dirt nap serious.
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Edit: sorry @superbee, see you've also explained it!
That's my new phrase, love it