The words moue, moo sound the same but have different meanings and spellings. Why do moue, moo sound the same even though they are completely different words?
The answer is simple: moue, moo are homophones of the English language.
To emit the deep, bellowing sound made by a cow; low.
The lowing of a cow or a similar sound.
A small grimace; a pout.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.