So BBC America posted a video to their YouTube page a month ago.

It's a Behind the Scenes on how they filmed the show's four clones dancing together.

This is from Season 2 Finale, so be warned, you may find spoilers!

The video is interesting enough, you can watch it and join everyone in the world as you are once again reminded it's just one actress!

Video Link:

Thumbs up for Tatiana Maslany