Question: Does anybody know how they did the scene where Mary Poppins is doing a duet with her mirror image?
Chosen answer: They recorded her singing in two separate parts and fixed them together. The editors did a good job on it! It may have been made a long time ago but even then the technology was quite advanced enough to carry out that scene.
Question: Higgins presumably knows about the ball's high standards of dress for men and women. Why then is he the only man there who is not wearing white gloves (which are routine for such occasions)?
Answer: It's a kid's show, not Game of Thrones.