Eyeline
Where a character's gaze goes, and whether the cut agrees: looks that meet across shots, or a scene that quietly falls apart.
Eyelines stitch separate shots into shared space: she looks frame-left and slightly up, so his answering shot must look frame-right and slightly down, or the two are no longer in the same room. The audience polices this geometry unconsciously and bills all violations to the scene's credibility.
On set, eyelines are protected with marks and stand-ins beside the lens; the camera's distance from the gaze also sets intimacy, the closer the look passes to the lens, the more the audience sits inside the conversation, until looking into the lens breaks the wall entirely. Direct address is the eyeline's nuclear option: our traveller spends one only at the very end.
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