2+2+2 = 6 - It's as simple as that.
BTW it is a great pickup line to ask her if she wants a "six lip smile" (most women get it right off the bat, most men can't count like that - so the lady knows that you know what your talking about, especially if you get called on to name the six lips, and you can). After/before you do a combination of a purr & a low growl in a ladies ear ask her if she wants to have some six lip smiles. Sometimes just the growling does it. Hehehehe!