City Lights - the Moving Flower
In the poignant closing scene of "City Lights"
as the former blind flower girl meeets her surprising benefactor, the camera switches back and forth from the girl's face to Chaplin's---in 2 or three shots when the camera's on Chaplin, he is chewing on the petals.
However, when the camera switches back to the girl, two or three times, the flower is down and to the side of his face.
This is supposed to be in real time, so Chaplin couldn't have made the change without it being noticed.