There is no single famous source behind this clip, which is part of why it works so well as a general reaction sound. Short human imitations of animals circulate widely on soundboards and in messaging chats, where a quick, recognisable bark can stand in for excitement, begging or playful teasing without needing any context. In Portuguese, the dog sound is traditionally written as au-au, and this a-au version plays on that familiar spelling with a more sung, comedic delivery. Creators keep returning to it because it is short, instantly understood and easy to drop into almost any funny moment.