You've been sharing a bed with the same partner for years. By now you know each other's sleeping habits inside and out, right down to the exact room temperature and sleeping position preferred. But how well do you know what it takes to turn on your partner? There's one way to find out -- by sharing your most intimate sex fantasies. An open exchange of erotic fantasies can help rekindle the flames -- or can they? Here's what sex experts say on the subject.