The Anal Stage, according to Sigmund Freud, is the period during which children – having left behind the nipples and bottles of the oral stage – become fixated on all things butt related. During these years, no toot goes unremarked upon and undelighted in. Freud saw this stage as ending ideally around the age of three, but most parents know that this phase is a much longer one and may in fact be endless.

In Stinky Science, the new non-fiction picture book from Toronto author Edward Kay and Georgetown, Ontario, illustrator Mike Shiell, young people’s obsession with the malodourous side of life is conceptualized not so much as a psychosexual stage but a critical evolutionary trait that all humans share. Having a keen nose for the difference between the fetid and the floral, argues Kay, has helped humans survive for millennia.

Kay aims to turn young readers into “scholars of stinks.” He covers the basics of the human olfactory sense (carried out through scent receptors that send signals to our brains) and why it exists (to identify edible food, detect threats, etc.). We get brisk, easy-to-follow explanations of – among other things – why rotten fish reek, how vultures locate carrion, why feet can smell like cheese, and what we are smelling when we get a whiff of poop. Kay doesn’t skimp on the important business of farts, though he always sticks close to the second word in the book’s title, exploring the chemical structure of broken wind, as well as noting the many animals that expel gas as a defensive move.

While Kay – who’s also a children’s TV writer and producer – keeps things relatively sober and science-minded, Shiell’s colourful illustrations go all in on the pee-yew: his human figures are grotesque, pig-nosed, and prone to flatulence. The very pages of the book are spattered with filthy blotches. I can only assume a scratch-and-sniff edition was too expensive to produce.

Stinky Science, which contains a glossary of odorific terms, packs a lot of information into its 44 pages. But let’s be real: kids will be drawn to the book for its more pungent thrills.