Popol Vuh by Francisco Ximénez

Then they left, each with his blowgun, and descended to Xibalba. They quickly went down the steps, passing through various river canyons. They passed through the midst of many birds. "Flocks" was the name of the birds.

And again they passed over Pus River and Blood River. In their hearts, the Xibalbans had intended these as traps. But they were not troubled. They just passed over them, floating on their blowguns.