He doesn't know he's making that sound and it's making him mad.

Buck the puppy is an 8-week-old Heeler. Like all puppies, he thinks he's a full-grown wolf who has to defend himself and his family from any possible dangers. And what could be more dangerous than a mysterious, uncontrolled noise coming from his own body?

This is like watching a dog chase his tail, but even cuter because it's a puppy and he's chasing his own insides. If he could, I bet he'd travel into his own body Fantastic Voyage-style. That's what a warrior Buck is.

Sources: Matthew Kennelly