Why on Earth? Candiru fish.
I’ve heard there’s a little fish that lives in the Amazon which can swim up streams of urine and lodge itself inside a penis. Sounds painful - but is it real?
Amazon Indians fear one fish more than the piranha - the candiru, a tiny transparent catfish some 50mm long and only 5mm wide. Looking for a host that will shelter it from predators, the candiru feels perfectly at home inside the urinary tracts of both men or women. Attracted by the flow of urine or menstrual blood, it quickly makes its way inside the penis or the vagina. The unwitting new host will feel a slight, almost sexual, tickling sensation at this point - followed by excruciating pain as the catfish raises lines of viciously-pointed spines along its back and jams itself firmly in place.
There are only two cures - amputation of the penis, or the insertion of small fragments of either the rare Xaqua plant or the buitach apple, which not only kill the fish but actually dissolve it. The best defence against the candiru, though, is simply not to fly all the way to the Amazon to take a leak.