It's such a big deal that a body double was used for 4 milliseconds, and during that time, she flipped her hair and walked.
Britney herself did all the other scenes and all the dancing. She probably had a tight schedule, she was finally promoting that week and shooting that MTV mini-documentary, and had to leave earlier, and they didn't get the part where she twirled around so the double did it.
Anyways... video of the year.