The image on the cover of Regular Expressions Cookbook is a musk shrew (genus Crocidura, family Soricidae). Several types of musk shrews exist, including white- and red-toothed shrews, gray musk shrews, and red musk shrews. The shrew is native to South Africa and India.

While several physical characteristics distinguish one type of shrew from another, all shrews share certain commonalities. For instance, shrews are thought to be the smallest insectivores in the world, and all have stubby legs, five claws on each foot, and an elongated snout with tactile hairs. Differences include color variations among their teeth (most noticeably in the aptly named white- and red-toothed shrews) and in the color of their fur, which ranges from red to brown to gray.

Though the shrew usually forages for insects, it will also help farmers keep vermin in check by eating mice or other small rodents in their fields.

Many musk shrews give off a strong, musky odor (hence their common name), which they use to mark their territory. At one time it was rumored that the musk shrew's scent was so strong that it would permeate any wine or beer bottles that the shrew happened to pass by, thus giving the liquor a musky taint, but the rumor has since proved to be false.

The cover image is from Lydekker's Royal Natural History. The cover font is Adobe ITC Garamond. The text font is Linotype Birka; the heading font is Adobe Myriad Condensed; and the code font is LucasFont's TheSansMonoCondensed.