Of all the ways to die, the most ignominious demise is having a kappa — or a Japanese demon — pull a magical orb out of one's asshole. You can repel the beasts with a burst of powerful flatulence, but you must be certain that your fragrant blast is muscular enough to bowl them over like ninepins.
The Harry Potter novels may have eschewed this life-or-death detail, but this is the gassy lesson centuries-old Japanese artwork imparts to us.
The kappa is a water sprite that has been a stalwart of Japanese folklore for hundreds of years. The kappa loves noxious flatulence almost as much as it enjoys gobbling people's innards by first reaching into their buttholes.
Fortunately, humans can repel the creatures by blasting them with gusts of their own anal zephyrs.
Just consult Tsukioka Yoshitoshi's (1839-1892) ukiyo-e work "Farting at a kappa at the lumber yard in Fukagawa" (above). This illustration will change the way you look at 19th century Japanese lumber yards forever. Click on it to admire a timeless slice of art history.
Be forewarned that kappas also can return the gassy favor — see this 1863-1866 woodblock print by Kawanabe Kyosai, "The Water Imp's Fart," which can also be translated idiomatically as "good for nothing." As in, those fishermen are "good for nothing" because they've been knocked off their boat by a rectal typhoon.
Should you engage in sonic warfare with the kappa, don't let it get too close. If the beast gets its paws on you, it will remove your shirikodama, a mythical, mysterious ball of anus meat that may (or may not) grant wishes or be sacrificed to a snake-dragon deity.
In any case, losing your shirikodama is unpleasant, as this 1797 illustration by Jippensha Ikku demonstrates. Here's a slightly NSFW picture by manga artist Mizuki Shigeru that also details the process.
The kappa's zeal for butt orbs is so fervent that you can fish for the monsters. All you need is a trapeze and a willingness to go commando, as this piece — "How To Catch Kappa" — by Katsushika Hokusai (1760-1849) demonstrates.
If this sounds too complex, you could always appease the kappa with a cucumber or trick it into bowing, a tactic that empties the vitality-giving pool of water on its skull. But where's the fun in that?
If you're really in a pinch, you can attempt to borrow a wild boar's anus. Utagawa Kuniyoshi imagined such a scene. Will this work in reality? Dubious. Kuniyoshi also imagined giant skeletons with ossified boners (NSFW). Take that as you will.
Utagawa Hirokage also designed this scene of a fellow peeing in a kappa's bowl. Is this a friendly gesture? We're not positive. Art historians, please chime in.
According to this NSFW woodblock print, anyone with the power to urinate with the force of Old Faithful will keep his or her shirikodama in working order. If you're still confused about the morphology of kappas, see this post on Pink Tentacle. And remember, fart scrolls — that is all.