The unreliable narrator in Coherence
This film has a particular kind of unreliable narrator - the unreliable camera. The convention in cinema is that contiguous shots of a scene in a movie are indeed of the same scene. This convention isn't respected in this movie. Many single scenes are intercut montages from multiple realities with moments inter-spliced with one another. There are all sorts of clues (which drove Vlad_the_Reviewer mad with frustration because they look like glaring "continuity errors" (see his timeline which he has loaded up on this forum)). They aren't.
Subtle changes in these different realities include:
(i) Bread cut? in the first kitchen scene we see Mike cutting the bread. A few moments (and a camera shift) later we see the bread again in the background - uncut.
(ii) Cheese out? One shot no cheese - next shot cheese on counter
(iii) Mike's shirt blue/black or grey/black? [This may be colour constancy problem with film stock]
(iv) Mike's second button - undone or buttoned up?
(v) Was Hugh wearing a coat when he came in? (Some realities yes, some no). Was collar down or up?
(vi) Kevin and Emily kiss & hug immediately or hug awkwardly after he has greeted others?
(vii) Coat rack and shelf by the front door. Keys on right hook, middle hook or missing? sunglasses on shelf, or candle or nothing?
Lauri's apparent serial faux pas is not only a glaring example that some people are already in the wrong universes but also we are seeing multiple versions of a scene. First she asks Mike about his career (Roswell etc), during which conversation it becomes clear she is in the wrong reality (not a yoga teacher, different actor played Roswell) and she manages to upset her host in the process. As she is about to start that conversation, you see the coat rack behind by the door - no sunglasses, car keys hanging on middle hook. Despite the obvious embarrassment she caused, she now turns to Emily and asks the same question ("what do you do now" ballet disaster etc) and makes a second massive faux pas. Except it isn't a second one. Just before she speaks to Emily, you see the coat rack behind her. Now there are sunglasses and the keys are hanging from the right hook. She doesn't make two social clangers one after another - she makes slightly different ones in two different realities. This forking / montage of realities is happening the whole time - sometimes signalled by a cut to black, usually not.
Did the director play fair - do we see Emily only in one reality at a time (i.e. we are always seeing "Emily1") as he claims? Almost. Emily's first house has sunglasses + keys on the right hook, and I don't believe we see her talking in another reality in that scene (certainly the director plays fair in the Roswell incident - you just get a momentary movement of her head in shot but no dialogue). However, Mike's shirt goes from blue in scene 1 to grey in scene 2 when Emily 1 is talking but this might just have been a colour constancy problem with the film stock. In later scenes the coat rack stuff bounces around constantly which might or might not be fully consistent - very hard to tell if the rule is that when Emily talks we are in Emily 1's reality.
Once you realise that even single scenes are reality montages, the film REALLY starts to do your head in.