Mirror Camera Shot

In the movie Contact there is a scene of the young girl running up the stairs to get her father’s medication from the bathroom. It turns out it’s shot from the mirror, which we see when she reaches for the medicine cabinet. However, there’s no disruption or cuts from the shot when it started out down the stairs and around the corner. Can’t figure out how he did this shot.

Does anyone know how this camera shot was done?

Here is an explanation (along with a clip of the shot):

“a Steadicam person with the Vista Vision camera strapped to his chest ran backwards in front of Young Ellie as he goes up the stairs and down the hallway – there was a speed change – we ramp from 24 to 48fps (though I can’t remember exactly – we could have ramped through three different speeds) – by the time she stops and puts her hand to open the medicine cabinet door (”A" plate ) – we are then inside the reflection. The medicine cabinet was the “B” plate (second plate) and then the door closes and we have the “C” plate (third plate) which was the reflection of the photo of Young Ellie and her dad. B"

or, in simpler terms, “the shot was filmed normally and flipped in post to achieve the mirror image. The actual bathroom mirror was replaced with a bluescreen into which the original shot was superimposed.”

Thank You!!!

Thank You!!!