How am I supposed to know whether this sentence is "Ils mangent les noix" or "Il mange le noix? They sound the same, right?
Does a REAL difference in pronuntiation of "ils mangent" and "il mange" exists? or we have to keep wondering about?
Nope. The pronunciation for "il" and "ils" is the same. Sometimes you can tell which one it is by the context of the sentence. For example, if you hear "ils sont", it must be "ils" and not "il" because you would've heard "il est" instead.