"Cliff Hanger and the Yodeling Yellow Yak" is a book in The Adventures of Cliff Hanger series by Livingston Dangerously. It was meant to teach the letter "Y".
Cliff is hanging from the cliff once more, when he suddenly spots 2 scientists looking for a yodeling yellow yak. Cliff reaches for his survival manual and learns that if 2 scientists are looking for a yodeling yellow yak by your cliff, put of a yellow yak costume and start yodeling. Cliff finds one in his backpack and begins to yodel. One scientist is overjoyed and almost takes him back to the lab, but then the other reminds him that they should just leave it in its natural habitat. Cliff takes the costume off and says he's not really a yak, and the book ends.