I saw this video on Facebook and it freaked me out, but I loved it.  It's an optical illusion.  These girls are dressed in black and white and you can't tell whose leg belongs to whom.  It's her leg! No, It's her leg. No, wait, how did they do that. Check out the video courtesy of YouTube.

According to the story on YouTube, the song is officially German and is called "Hiss - TANZ" . This dance style is called Strumpfhosentanz and if you do a google search of that and hit videos you can find other videos of people doing it.