What Does the Fox Say?

Spotted this furry fella scampering through Capitol Hill. I don't think it's actually a fox, it's just the first animal I thought of. Perhaps a mythical beast. With armor. Who got the PAX West dates wrong. Capitol Hill Seattle cosplay costume mythical

The image reminded me that I'd heard the phrase "what does the fox say" before. I assumed it was a children's book. There might be a children's book by that title, but it can't match the popularity of the music video I found. I think I might be the last person on the planet to have watched this. It's pretty bizarre but also funny and clever.