When breasts get to a certain size, some of us go crazy: our hearts beat faster, and there is a "pull" deep in our chests of crazy excitement and deep desire. It differs for different people, I'm sure. I know that Lilly has reached this size, for me, and that every cupsize she swells bigger only drives those of us who are thus effected, even crazier with lust. It's what breast expansion is all about.
Others apparently have no clue.