The blue-footed birds with the funny name do put in cameos but are not the subject here. With tongue so firmly in cheek that it may be hard to extract, Vo plays deliriously with words and expectations but also delivers a frank overview of mammary glands across (relevant) species and even (as pictures of stylized but unmistakably female figurines from prehistoric Austria, the Cyclades, and Ghana demonstrate) the ages. Repeating the titular sobriquet as often as possible, she explains what they're for (even adding a mention of plant-based milk) and notes that different mammals have different numbers of breasts, from a cow's four "booby tubes" ("Udderly fascinating!") to a mother dog's 10. Humans, she writes, have two, and they are called "breasts." The stencil art is highlighted both by an image of a dark-skinned human adult breastfeeding an infant and, to suggest the wide variety of breast shapes and sizes, an entire page of them rendered as daubs and dots--mostly in pairs but including representations of single and double mastectomies. Human figures elsewhere are diversely hued and discreetly posed or clothed. Along with transforming any future mention of the Grand Tetons into an occasion for giggles ("There are mountains that some say are named after boobies"), this disquisition will turn young audiences into expert "boobiologists." (This book was reviewed digitally.) A funny and nutritious flow of information. (source note) (Informational picture book. 6-10) Copyright (c) Kirkus Reviews, used with permission.