At the autopsy of the Bunker twins, one of the anatomists opined that their active sex lives had “shocked the moral sense of the community”—even though the truth is that the Bunkers’ neighbors appeared to have just accepted the situation. A little-known fact is that the Bunker wives’ father had originally objected to his daughters marrying the twins not because they were conjoined, but because they were Asian. (This was, after all, the antebellum American South.)

Yet in the 19th century, when doctors discussed whether the twins Millie and Christina McCoy could marry, one spoke for many: “Physically there are no serious objections ... but morally there was a most decided one.” When, in the 1930s, Violet Hilton sought to get a marriage license while conjoined to her sister Daisy, she was repeatedly refused.

The same discomfort generally carries through to our own time. When the filmmaker Ellen Weissbrod set out to do an A&E program about Lori and Reba Schappell, who are conjoined at the face, Weissbrod showed raw footage of the twins to New Yorkers on the street, without explanation, to gauge their reactions. Upon figuring out what she was looking at, one woman said only, “I mean ... sex ...”

Sex is often mentioned by commentators on conjoinment as one of the beautiful things supposedly made instantaneously horrible by being conjoined. I’m afraid I just laughed when, in writing a book on conjoined twins, I came across this 1984 line by a nurse writing in a medical journal: “Two people never being able to obtain privacy to bathe, excrete, copulate, or eat defies imagination.”

Surgeons sometimes openly allude to sexuality as a motivator for separation surgery. In 2002, as soon as he had made the cut separating two little girls joined at the head, the neurosurgeon involved paused to announce to the assembled medical team, “We now have two weddings to go to.” Indeed, when I talked to contemporary surgeons about how they decide whether to undertake the substantial risks some separations involve, I found that surgeons had two fears, sort of conjoined: one, that twins would grow up conjoined and thus never have sex; two, that twins would grow up conjoined and actually have sex.

Believe it or not, surgeons have done this: Separated toddler twin boys and made one a girl because there was only one penis to go around. (These children were essentially two people on top and one on the bottom.) In fact, this has been done in two cases. In one case, the “girl” is said to have reverted to being a boy, and in the other, the child left as male died, leaving the parents who had come to the hospital with two sons to go home with one daughter. Yes, this was considered better than leaving the children alone.

So I suppose I should get to what the people really want to know: What do conjoined twins feel when they have sex? If one is sexually stimulated, does the other feel it? If one has an orgasm, does the other enjoy the same, however unwittingly?