Forgive me if I start off the new year with this rather filthy post.
A couple of weeks ago my wife and I spent the weekend in
a lovely hotel in Taipei, a modern thing with ample white-wallage, funky lighting, an all-controlling remote and the bathroom conceived as a walk-in glass box.
After doing so, I was very excited to discover that the toilet was, in fact, an electronic gizmo developed to auto-clean one's ass:

Figure 1
"Paper tends to distribute the problem"
This is what they say on
www.washlet.com, a site selling a similar product to the one I tested. The idea being that a strong, focused jet of water aimed precisely at the anus does a much better job than the traditional toilet paper wipe.
Did it work? Well, yes and no. Having only tested it once I don't have enough data for a precise conclusion. What I can say, though, is that to achieve 100% cleanliness (and I won't say "so clean that you would want to eat off it") one should follow a diet consisting primarily of Wheetabix. Also, the system does not feature a feedback mechanism (eg. a cam connected to an LCD screen on the console) to determine whether a satisfactory level of cleanliness has been achieved. One ends up using toilet paper to check for residues anyway.
First use can be traumatic
Unless, of course, one is used to being poked in that spot. I am not.
The jet of water felt like it had the kinetic strength and temperature of a mini-tsunami originating from the antartic. A high-pitched squeel was inevitable.
For testing purposes I tried the pushing the women-only red button (see Figure 1 above). Scrotum sensitivity allowed me to acertain at what distance from my anus my vagina would be positioned had I been born female.
The anus constant (along the X,Y,Z axis)
For the product to be viable the water jet must be able to bullseye the anus each time. This means that every person in the world, no matter what size, height and bone structure, ends up with their anus in the same position, spatially speaking, when sitting on a toilet. It's as if our bodies have been designed specifically for this dynamic. If evolution can't explain this then it can only be a matter of intelligent bidet design.