Alphitomancy
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Alphitomancy (from Greek alphito, 'barley', and manteia, 'divination') is a form of divination involving barley cakes or loaves of barley bread.
When someone in a group was suspected of a crime, the members of the group would be fed barley cakes or slices of barley bread. Supposedly, the guilty party would get indigestion, while all others would feel well.