After the rehearsal scene, when the pianist (Michel Legrand) says "self-pitying spoiled child," the shot is a composite. Michel's head and the background in front of him is one shot, and the background behind him is another shot, which pans towards Cleo after he speaks his line. The clocks on the ledge behind Michel can be briefly seen in two places at once.
The dolly track used in the final shot can be seen as the actors walk away from the hospital. Agnes Varda recounts in the much later documentary 'Anecdotes and Memories' how devastated she was to see the track and convinced the producers to allow a re-shoot at great expense. However none of the retakes matched the emotional quality of the original take so she retained it despite the goof.
In the beginning of Chapter 3, as Cleo is putting on a black hat, the camera-man's right arm can be seen in the mirror next to her.
As Cléo tries the penultimate hat in chapter 3, the camera pans round and you can see the cameraman in the mirror behind her.