This story comes from the Piaroa people of the Orinoco Basin in what is now Venezuela.
Long ago, the wives of the great hero Wahari were playing on a swing over a deep ravine in the jungle. Buoka, Wahari's dim-witted older brother, came by and "played" with them too. Buoka's most striking feature was his penis, which was so long that he could sling it over his shoulder. After swinging on the penis for a bit, each of Wahari's wives invited him to have sex.
This did not sit well with the great Wahari.
Using his magic, he changed himself into a beautiful woman . . . without a vagina. In this form, he skipped out to the ravine, immediately attracting Buoka's attention. From a far distance, Buoka shot out his penis to violate him/her. The lack of a vagina did not dissuade him. He tried with her thighs and belly-button but could find no opening (Buoka, it would seem, had never been to prison). Annoyed at his idiot brother, Wahari sliced the giant penis into five pieces so the remaining stump was regular-sized but gushing blood.
In shame, Buoka went to hide in his house. When Wahari came to check on him, Buoka told him that he was indisposed and could not come out. Wahari's wives went back to the swing to look for Buoka but, unable to find him, went home. When they asked about his brother, Wahari told them that "it was that time of the month."
The women, or anyone but the two brothers, had no idea what that might mean.
The wives all went to Buoka's house and had sex with him, taking the bleeding from his penis and forever giving it to all women. From that day forward, menstruating women could not so much prepare food for a man or he would sicken and die.
The five severed pieces of Buoka's penis changed into snakes and forever search the jungle for human women to have sex with, a warning for young girls who might venture too deep into the woods.