I know these videos have been out for a few months already but I just found out about them the other night. Still, it's pretty damn cool.
The first video is the trailer for "The Hobbit: The Desolation of Smaug" followed by the reaction video of Alex (Kili) and Kellie (Fili) of Happy Hobbit. They are huge fans and apparently were VERY excited about the new trailer. Well, apparently word got to Peter Jackson and the cast about the video and they decided to film their own reaction video to the girls' reaction video. Then the girls found out and filmed another reaction video to the crew's reaction video of the girls' reaction video to the trailer for "The Hobbit: The Desolation of Smaug".
Confused? I know I am.
I heard about this on Late Night with Jimmy Fallon. Orlando Bloom was there promoting his play "Romeo and Juliet". At the 3:12 mark he mentions the girls and their video.