Barium
Images from a double-contrast oesophagram.
There is background granularity to the normal smooth-as-glass appearance of the oesophagus, compatible with reflux oesophagitis.
That's not all there is, though... at the gastro-oesophageal junction, there is a fine reticular pattern superimposed on the granularity. This pattern is concerning for Barrett oesophagus, which this turned out to be on EGD and biopsy.