There is no widely documented source for Brain Weasels Rawr, and it appears to have surfaced as a user-uploaded soundboard clip rather than a line from a show or game. Its appeal comes from the internet's love of tiny, fake-ferocious creature noises that work as flexible reaction audio. Creators tend to reach for it when they need something playful but slightly wild, somewhere between a pet sound and a cartoon monster, which keeps it circulating in meme edits, stream alerts and short-form comedy.