Before their descent into Xibalba, Hunahpu and Xbalanque had already dealt with a domestic rivalry at home: their older half-brothers, One Batz and One Chuen, gifted musicians, singers and craftsmen in their own right, treated the twins with jealousy and contempt, mistreating them and mocking their hunting. When Hunahpu and Xbalanque finally retaliate, they trick the older brothers into climbing a tall tree to retrieve birds the twins have supposedly shot down, then cause the tree to grow impossibly tall so the brothers cannot climb back down, and the two, in their frustration and shame at being stranded, are transformed into monkeys, their fine clothing becoming fur and their faces stretching into a simian shape. When their grandmother laughs uncontrollably at the sight of her transformed grandsons, the twins deliberately let the two escape into the forest for good rather than restoring them, since her laughter proves she finds real amusement in the misfortune of the sons she had always favored.
Some scholars connect this episode to the Maya reverence for skilled artistry, since One Batz and One Chuen's names are associated with craftsmanship and the arts, and their transformation into howler and spider monkeys, animals genuinely known in the region for a certain restless, chattering energy, was sometimes read as an origin story explaining the existence of these two monkey species while also settling accounts within the twins' own family before their far greater trial against the lords of Xibalba begins.