Commonly known in the United States by its chorus “What Does the Fox Say?” I was introduced to this song by my then-nine-year-old niece who showed the video on their television through their AppleTV.  She was quite taken by it; I assumed it was just a kids’ thing of some sort.  Imagine my surprise to hear this on the radio on a Top 40 station.

A better explanation of just what this is can be found written by Paul over at House To Astonish:

 This has been floating around on YouTube for a month now, going viral in other countries and waiting to do something in the UK.
I’ve seen people comparing this to “Gangnam Style”, which misses the
point, really.  ”Gangnam Style” was a proper record which went viral in
large part because the added dimension of incomprehensibility provided
by a language barrier and a very specific set of cultural references.
 ”The Fox”, on the other hand, is a perfectly intelligible comedy sketch
which wasn’t even intended for release – it’s a trailer for a Norwegian
TV show (hence the time and date at the end of the video).  Ylvis are
brothers, and are apparently pretty well established in their home
country.  If this track sounds surprisingly professional for a novelty
song, that’s because it’s produced by Stargate, which itself is meant to
be part of the joke.  Ylvis do a lot of parody songs on their shows

That very much explains everything.  So in the United States this duo has likely been seen as something quite different than the intention for their original audience.