(at around 1h 25 mins) During the film's final scene, The Tramp is seen holding the flower to his face when seen from the front; when seen from the rear, he is holding it to his lapel.
In the famous fight scene, several spectators in the back row(s) of the gallery are motionless, either painted on a matte painting, or cut-outs or mannequins. In the shot of The Tramp dreaming of the flower girl, and the following shot with the trainers again kneeling around him, we see a particularly obvious mannequin or statue, a man in a light gray suit, in the lower right corner of the screen. He also is visible in other scenes.
(at around 50 mins) When the man swallows part of the Tramp's soap and starts spraying bubbles, the tube used to spray the bubbles is clearly visible behind him.
(at around 39 mins) When the Tramp accidentally swallows the whistle, his real eyebrows are visible beneath his fake ones. This was done intentionally to give him a lopsided, intoxicated facial expression.
(at around 1h 9 mins) When the Tramp is knocked out on the table in the locker room you see a pair of boxing gloves hooked on a post behind the table. The Tramp wakes up and struggles to sit up. The entire scene you can clearly see a wire attached to one of those gloves that when triggered, falls on his head, knocking him out once again.
(at around 32 mins) When the Tramp takes the girl home, the birdcage outside the window is gone, but later reappears.
(at around 1h 19 mins) When handcuffed to go to jail, the Tramp's left hand is cuffed, but when arriving at the jail, it is his right hand that is cuffed.
(at around 1h 13 mins) When the Tramp tries to place a gun in the desk top table, the Millionaire is lying back on the sofa. The next shot, he is sitting upright.
(at around 1h 5 mins) In the boxing match when the Tramp propels himself off the ropes (twice) at his opponent. You can clearly see the wire on the back of his trunks.
(at around 14 mins) When saving the man's life, and trying to climb out of the water, the position of the Tramp's hat is inconsistent.
(at around 1h 12 mins) When the Tramp and the Millionaire are drinking champagne with the burglars in the house, the Tramp places the glasses on the table behind them. When one of the burglar come up behind them the glasses are gone.
(at around 31 mins) When the Tramp buys all of the flower girl's flowers, she wears black stockings, but when he brings her home immediately afterward, she wears tan stockings.
Some of Charlie's curls are darker than the others, caused by Chaplin applying dark hair dye on his gray curls, a luxury a tramp like Charlie could hardly afford.
In the famous final scene where the blind woman and Chaplin are staring at one another, the flower Chaplin is holding is seen to move from being held in his hand against his chest to slightly in his mouth between over the shoulder shots at the blind girl and the shots at him.