On the planet Thwart, the dominant species is much like humans: bipedal, bilaterally symmetric, two sexes.
As with us, there are some male Thwarts that are sexually attracted to other males, and similarly for females. As with us, their society had a problem with that for awhile, but they got over it and now nobody gives it a second thought.
But there is one large physical difference from us: with about a fifty-fifty split, Thwarts have either a face that is on the front side or on the back. Since they're used to it, their culture and infrastructure have been built to accomodate it. But it does cause one big problem: "spooning" with a lover, which they enjoy as much as we, is thought to be normal only between two "fronters" (like humans) or two "backers".
As with sexual matching, there is a minority that doesn't go
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