Correcting from your English...

How does "吹牛（chuīniú）" come from come about?

"吹（chuī）牛（niú）" literally means "to blow cow","牛（niú）" means "cow". [However, you must watch out in using the word "blow" because in some context it means a sexual act, eg "to blow someone"  However, it is okay to say "I blow you a kiss"] "吹牛(chui1niu2)" in Chinese Figuratively it means "to boast; to talk big". But How does this come about word come? It is saying that This stems from the practice in the old days when the butcher will cut would make a small slit on a the sheep's carcass after the bloodletting.  The carcass is then inflated by  and blowing into it. into the sheep's body until the body is inflated up. After this, that, the butcher will rip it slightly with a knife, and the skin will would break up. But Now if somebody would say that he can blow up a cow's skin, then he is exaggerating too much talking big. because not only the carcass of the cow's is too large but its skin is not only big but also firm, it can't to be blown up by a human mouth!be blew up at all. So "吹牛（chuīniú）" Hence "to blow a cow" becomes a word that means "to talk big".

”吹“的意思是“to blow"，“牛”的意思是“cow”。汉语中的“吹牛”意思是“boast; talk big"。但是它是怎么来的呢？据说从前宰羊时放完血，屠夫会在羊的腿上割开一个小口，把嘴凑上去使劲往里吹气，直到羊全身都膨胀起来，用刀轻轻一拉，皮就会自己裂开。这叫吹羊。如果谁要说可以把牛皮吹起来，那就是说大话了，因为牛皮很大，而且非常坚韧，根本吹不起来。所以“吹牛”就变成了说大话的代名词。

How does "吹牛（chuīniú）" come from

"吹（chuī）" means "to blow","牛（niú）" means "cow". "吹牛(chui1niu2)" in Chinese means "boast; talk big". But how does this word come? It is saying that butcher will cut a small slit on a sheep after bloodletting and blow into the sheep's body until the body is inflated up. After that, the butcher will rip slightly with a knife, the skin will break up. But if somebody say he can blow up a cow's skin, he is talking big. Because cow's skin is not only big but also firm, it can't be blew up at all. So "吹牛（chuīniú）" becomes a word that means "talk big".

”吹“的意思是“to blow"，“牛”的意思是“cow”。The meaning of ”吹“ is "to blow" while the meaning of “牛” is "cow"  汉语中的“吹牛”意思是“boast; talk big"。In Chinese, it means "to boast; to talk big" 但是它是怎么来的呢？据说从前宰羊时放完血，屠夫会在羊的腿上割开一个小口，把嘴凑上去使劲往里吹气，直到羊全身都膨胀起来，用刀轻轻一拉，皮就会自己裂开。这叫吹羊。如果谁要说可以把牛皮吹起来，那就是说大话了，因为牛皮很大，而且非常坚韧，根本吹不起来。所以“吹牛”就变成了说大话的代名词。