"First, modern maize pollen grains are larger and turn red when stain is applied, whereas ancient grains do not, " they said.

BBC: Maize was key in early Andean civilisation, study shows

The shavings were then immunostained bathed in a special reagent that would mark the presence of abnormal proteins with a bright, telltale red or brown stain on the surface of the tissue.

NEWYORKER: Offensive Play