There is no widely documented original video or creator behind this phrase, so it is best understood as an Italian TikTok reaction sound rather than a line from a film or show. The Italian words are simple enough to travel: cavallo means horse, while un cazzo is a crude, emphatic way of saying nothing or no way. Creators use it to puncture bragging, excuses and unlikely stories, often with a horse image or a deadpan stare. Its short length and blunt delivery have helped it circulate as a reusable sarcastic reply across short-form video.