While the quartet is assembling to practice in the beginning of the movie, Daniel is asked to give a first violinist a listen, Daniel says he will. He looks to Juliette, who agrees that's a good idea. She is shown with her bow at waist height, but in the next shot she is holding it in front of her face.
The goof item below may give away important plot points.
When Robert closes his music at the end of the film, we see him begin to close the booklet with his bow in his hand. The close up shows him clearly NOT holding his bow, yet, in the next cut he is holding his bow again.