Lesbian and bisexual women are more likely than totally straight women to say they've had anal sex with a man.
Here's my best guess: In many if not most cases, openness to experimentation is driving everything else. Adventurousness makes a woman more likely to try various sex acts with men. And at the same time, it makes her more likely to express interest in other women. ...The unkind way of putting this, from a liberal point of view, is that women who claim to be exclusively heterosexual are, on average, more conventional or uptight than women who report having some interest in other women. These "exclusively" straight women might not even be exclusively straight. They're just obtuse to their wayward feelings, or afraid to admit them. The equally unkind view, from a conservative perspective, is that sexual mores are collapsing in all directions.