The eye can make tears without an emotion
Tears are not a single-purpose signal. The eyes constantly produce a thin film that keeps their surface moist, and they also have a fast protective response: when an irritant reaches the eye, sensory nerves signal the tear glands to flush it away. Menthol vapor can set off that reflex, so the visible result—wet eyes or tears running down the face—does not require the actor to feel grief.
That distinction matters on a film set. An actor may be able to play a scene’s emotion convincingly but not produce tears at the exact moment a camera needs them. Conversely, real sadness does not guarantee tears on cue. A practical effect can provide the physical detail the camera needs while the performance carries the character’s feelings.
A small effect with limits
Tears are only one part of a believable crying scene. The actor still has to coordinate expression, breathing, voice, and timing; makeup and continuity teams also need the look to remain consistent across takes. A reflex can create moisture, but it cannot supply those choices.
Because the effect works by irritating the eyes, it is a controlled production tool, not a measure of how upset someone is. The useful trick is the separation between the appearance of crying and the feeling of sadness—a distinction that lets a scene be performed repeatedly without requiring the actor to recreate the same emotion on demand.
