A Topological Look at Leviticus
R. Chicken, Really Adjunct Professa' of Arcana, Tha Ivory Tower
Only read this if your balls are open and you're not discrete.
The human body, from a topological point of view, is a surface, compact (because all of its boundaries are part of it and it is bounded in size) and connected (because, roughly speaking, we come in one piece -- I don't want to talk about open sets made of skin).
Furthermore, we're orientable. For each human, the world not on the surface of the human divides neatly into two pieces; those pieces inside the person (like xyr liver) and those pieces outside. It is of fundamental importance to recognise that everything in a person's digestive tract is outside of the human, from a topological point of view, because it can pass freely from xyr mouth to xyr anus or vice-versa without cutting the surface.
An important result in topology says that compact, connected, orientable Hausdorff spaces locally homeomorphic to the Euclidean plane are all basically equivalent to spheres with some closed loops of surface stuck on. In particular, a human, regardless of gender, contains a unique such 'handle': the one formed by the alimentary canal. In other words, we're all a bunch of tori.
Different sexual practices affect our topology in different ways. For example, when a good Christian man turns off the lights and inserts what god intended where god intended it in his good Christian wife, her topology is unaffected. From a topological viewpoint, she's got just as many holes in her as she did beforehand. However, if a godless deviant inserts anything at all into either the mouth or anus of another godless deviant, the receiver's topological hole becomes a mere dent and xe becomes homeomorphic to a sphere. We can conclude that godly objections to such deviant practices are no more than injunctions against inserting anything into a human surface in a way that affects the receiver's topological genus.
This betrays seriously bizarre sexual attitudes on the part of god. Rather than consider the topology only of the receiver, it is important to understand such activity, whether godlessly deviant or as god intended, as a union of two human surfaces rather than as some undefined action of one surface on another (we're not talking groups, after all). In that case, As God Intended Surface-on-Surface Action is no more than the taking of the connected sum of two tori, resulting in a single, topologically inequivalent surface. However, Plumbing the Alimentary depths creates a new surface from the two original tori, with one torus reduced to a sphere and the other still a torus (the Plumber's crack is invariant). This is homeomorphic to either of the original tori, so it is only in the case of godless deviance that true union occurs.
Exercise for the reader: Find someone willing and make xym non-orientable tonight!
Extra credit: What is the maximum number of human surfaces possible in harmonious-union-preserving topological orgies?