YouTube user Lars Von Retriever either has a lot of time on their hands, or they're a visionary, because this is the weirdest "cover" of "Holy Wars… The Punishment Due" by Megadeth I've ever seen. The song plays in the background normally, but taking over the focus of the riffs is Dave Mustaine laughing and edited together so it fits the rhythms.
Why? Because the Internet. Also, this shouldn't surprise you – remember somebody did the same thing with Metallica and James Hetfield's laughs and Meshuggah's "Bleed" with all the snare drum parts replaced by farts?