Two lips

A boss has to interview 4 girls for a secretary position. He asked the same question to each one of them.

Boss : “A woman normally has lips in 2 different places. What’s the difference between the two ?”

First Girl : “One is hairy, the other isn’t.”
Boss : “OK… good !”

Second Girl : “One can talk but the other can’t.”
Boss : “That’s better !”

Third Girl : “One is vertical & the other is horizontal.”
Boss : “Hmm.. clever !”

Last Girl : “One is for me & the other is for my Boss.”
Boss : “You are hired… !”