When Satine sings the line, "I hope you don't mind, I hope you don't mind... ." to the Duke, he is holding a wine bottle and she is barefoot. When she jumps on the bed, he is bottle-less and she wears shoes.
When Satine gets on top of Christian when they're in the elephant for the first time, his bowtie is sometimes on and sometimes off.
Before Satine sings the final "Come What May" there are tears streaming down her face and gook coming out of her nose. After the cut-away, her makeup is clean and her nose is beautiful.
During Spectacular Spectacular, as Toulouse is yelling "The greatest thing you'll ever learn is just to love and be loved in return" you see him start to grab the rope. When he starts to fall after Christian sings "Come What May" we see him not holding the rope, then suddenly he has the rope in his hand when he's falling towards the stage.
When Satie begins to play the piano in El Tango de Roxanne, Christian can be seen strolling along the sidelines of the ballroom. He passes the same man and woman three times, twice in a far shot and once close.
When the narcoleptic Argentinian has an attack of narcolepsy during the show and falls down the stairs to underneath the stage where Christian is sneaking through, the Argentinian lifts his head when Christian pushes him backwards to see his face. When asleep/unconscious, there is no way the person would like their head. It would stay down chin to chest due to gravity.
It has been suggested that the long white coat Christian is wearing on stage (the one he took from the Narcoleptic Argentinean) mysteriously disappears before he begins singing to Satine, but in fact we see him take it off as he walks down the aisle. It does disappear from the floor, but perhaps some helpful theatergoer picked it up while we weren't looking.
During the Green Fairy "Sound of Music" song, while Christian and the Bohemians are standing and singing outside of the "L'amour" apartment, Toulouse raises his leg and you can see a knee instead of his foot.
The scar under Warner's eye switch sides throughout the movie. In the scene where the Duke calls Toulouse "pig," it switches several times between cuts.
As Satine and Christian descend from the top of the elephant and enter the chamber inside, the hanging ornaments above the entrance can be seen to start moving by themselves - this is from the wires that the actors had to wear when atop the elephant but which were digitally removed from the image.
While "Spectacular, Spectacular" is being sung, it is clear that Toulouse is dragging his "feet" instead of lifting them.
When Christian kicks Toulouse out of his room, Toulouse reaches much too far down for the door knob. Since Toulouse is 4'11" the door knob would be around chest height, not waist height.
In the first scene we see a completed white domed church of Sacré Coeur atop the hill. The basilica was not completed until 1914, 14 years after the story takes place. (It is also shown directly across the Seine from the Eiffel Tower, which is northwest. It is actually northeast of the Eiffel tower and would not be visible in this view.)
In 1899, the artist Toulouse-Lautrec can be seen wearing a wristwatch. Men did not wear wristwatches until after World War One; until then they had pocket watches on chains.
Toulouse says "you're the voice of the children of the revolution", but his lips don't match the words.
During "El Tango de Roxanne", the Argentinian's shoes sometimes click on the floor and other times make no sound.
In the "Elephant Love Medley" scene, Satine and Christian are obviously lip-syncing. A few times, they miss saying the word all together, or they are just a part of a second behind the pre-recorded vocals.
Satine's caged lovebird "sings" like a canary.
When Satine says, "You're going to be bad for business", we see her from behind - but it is obvious her lips are not moving. (The remainder of the phrase, "I can tell", is shown from the front and her lips do move).
When one of the Bohos is swinging on the chandelier during "the pitch" in the elephant, he is being pushed by a crewmember wearing a wristwatch and a baseball cap.
A steadicam operator and another crewman is visible during the Can-Can dance.
During "Roxanne", a camera, and a crew member wearing modern shorts, are clearly in shot on the right-hand side of the screen.
In the final performance, the shadow of the camera crane falls on Satine's dress.
Cameraman's foot and leg visible in the background of the Can Can scene. (Seen in the Extended Can Can in the 2nd disc. Appears when the Can Can Girls begin to lay on the floor kicking their legs in the air.)
Satine goes to great time and effort to be bound into a red dress before her meeting with "the Duke". Why would she then change into the black negligee in which she arrives at the Elephant Room?
Satine's accent changes noticeably throughout the movie.
Christian repeatedly refers to the "magical sitar player" falling from the ceiling during the climactic scene. It's actually the magical sitar that falls, not the sitar player.
Satine tells Christian "The difference between you and I is..." while trying to break up with him, rather than the correct "between you and me".