In China, cameras scan student emotions, stoking new fears of state monitoring

> “It’s very difficult to label the underlying emotion,” he said, since external expression and internal feeling don’t always correlate well.

Not true. Paul Ekman spent most of his professional life studying micro expression and he developed pretty accurate system for recognising emotions leaking though micro expressions. The science presented in the TV series "Lie to me" was largely based on his work. https://www.paulekman.com/