At the risk of making a reference dated by a year or so, this video indeed shows what the fox says.
Melanie Galea was out at Fort McMurray Golf Club in northeastern Alberta, Canada, when she spotted a pair of foxes on the 10th hole. She decided to film them with her camera to see what they would do. The foxes had a bit of a conversation with each other, showed their teeth to the videographer and then decided to head to their next spot.
Ylvis now knows the answer to their question, and it's kind of terrifying.
Also, no word if Melanie is related to the disgraced Canadian doctor Anthony Galea.