How an onion can make eyes water
When onion tissue is cut or crushed, chemical reactions produce a volatile irritant that can drift into the air. If it reaches the eye, it activates sensory nerves that detect irritation. The eye responds by releasing tears to dilute and wash away the irritant—a protective reflex, not a signal that the person feels grief.
That distinction matters because the body can produce the same visible result for different reasons. Tears from irritation and tears associated with emotion may look alike on someone’s cheeks, even though their causes are entirely different.
Why the display could be convincing
People usually cannot see what caused another person’s tears. They infer emotion from outward clues: wet eyes, a trembling voice, a facial expression, and the surrounding situation. If those clues fit a funeral, observers may interpret tears as sorrow without knowing that an irritant prompted them.
This is a broader feature of social life: an expression is evidence about someone’s state, but it is not a direct view into that state. The cue can be genuine while the inferred emotion is wrong. In this case, the tears themselves are real; what they do not prove is that the person is grieving.
The trick’s effectiveness rests on that gap between what an audience can observe and what it cannot. A visible sign may be easy to produce, while its cause remains hidden.
