What a Workout
Even though Samantha’s magic happened with a wiggle of her nose, oftentimes for effect, the actress would motion with her arms for objects to move or things to happen. But since they used stop-motion filming and sometimes took long pauses to create the “magic” on set, that meant Montgomery’s arms had to stay up for long stretches of time.
This might not seem like much, but try holding your hands perfectly still above your head for ten or twenty minutes. Apparently Montgomery even had some sort of crutches to assist in keeping her hands up in place. Any change of position and continuity would be lost, so keeping them in place was important.