Legendary animal expert Jack Hanna finally has an answer to the question on everybody's mind this week ... telling us he ACTUALLY KNOWS what the fox says.
Ylvis posed the question ... so we wanted an answer -- and it turns out the guys from the group were pretty close.
Hanna says the animal makes a high-pitched squealing noise "almost like the sound a dog toy would make."
The animal wrangler tells us he's glad the group is getting people talking about animals ... but hasn't heard the song.
Now enjoy a video of Jack's favorite kind of fox getting all Joff-tchoff-tchoffo-tchoffo-tchoff.