While leafing through some old research papers, Hillary Elfenbein noticed something strange about the photographs in one famous study. The research from the late 1980s had asked volunteers if they were able to identify emotions in the faces of Japanese and Caucasian people. Some of the “Japanese” faces were posed by Japanese-Americans, the rest by Japanese nationals.

When Elfenbein herself looked at photographs, she realised that she could tell which were which. Her collaborator, Abby Marsh, found that she could too. So they ran an experiment.

They found that the Americans they tested were also strangely good at spotting who was Japanese and who was Japanese-American, even though they were all ethnically the same. The subjects wore the same clothes, and were lit in the same way. When the two groups held neutral expressions, people could barely differentiate between them. But when they showed their feelings, especially sadness, something from Japan or America seemed to emerge.