Nadal and Serena Walking on water

Hey check out this video...its pretty cool... no idea how they did it though! i thought they had been superinposed in the photos online, but this video shows otherwise!

http://youtube.com/watch?v=3AUpoYouQPo

Serena: "I like hard courts, I like grass courts, I like play courts, I can play on anything, including water".

What about clay??

:spit: