I know lyrics meaning is not a kind of a thing English SE is supposed to specialize in, but before looking for possible figurative meanings of the song excerpt that I put below I just want to reassure the phrase in bold is not a rare idiom or something.
There is a song by Pink Floyd - Arnold Layne. It has the following lines:
Oh, Arnold Layne
It's not the same, takes two to know
Two to know, two to know
Why can't you see?
What does (it) takes two to know mean? Is it an idiom?