The term 吹牛 (chuīniú), which literally translates to "blow cow", is believed to have originated from the practices of herdsmen or butchers along China's Yellow River. In one common folk etymology, when boasting about the size or strength of their livestock, individuals would exaggerate by claiming they could inflate a cow's hide by blowing into it, an impossible feat meant to symbolize empty bragging. Thus, the vivid image of someone trying to literally "blow up a cow" became a metaphor for making wildly inflated claims, eventually solidifying into the modern idiom meaning "to boast" or "to talk big".