3. Something they've never confessed.
Odds are there's a certain practice you or your partner would like to try. But you've always deemed it too far over the line, so you've never brought it up. A healthy relationship should be able to audition unusual ideas, even if they never make it onto reality's stage. Customary behaviors in this category include S&M, the use of sex toys, role playing, threesomes and paraphilias (fetishes such as wearing opposite-gender clothing, or rubber, vinyl or leather apparel).
Without question, many of these practices entail asking a lot of your partner. Still, you'd be surprised how common such fantasies are. Though Fifty Shades of Grey is fiction, many couples do in fact integrate "S&M lite" into their bedtime routine once one partner sincerely requests it. This might include being tied to the bed, being spanked, playing a submissive or dominant role in the bedroom, and any number of additional shades.
Gender-bending play (such as wearing clothes of the opposite sex) or nonmonogamous acts (such as bringing a third person to bed with the two of you) are unacceptable to most people. At the same time, flirting with these fantasies — watching an X-rated video that features a ménage-à-trois, for example — may make you feel more intimate, not less. You've already bared your body and your soul to your partner; if your relationship is solid and trusting, you should now be able to bare your thoughts.
Note: Some fantasies need to stay just that; no one should be pressured into doing something about which he or she has strong ethical reservations. But understanding one another's psyche can be very loving — and very sexy.