The book is written in anapestic tetrameter, Seuss's usual verse type, and illustrated in Seuss's trademark pen and ink style. The book is likely a tribute to a child's imagination, because it ends with a reminder that all of the extraordinary creatures exist only in McGrew's head. If I Ran the Zoo is often credited with the first printed modern English use of the word "nerd," in the sentence "And then, just to show them, I'll sail to Ka-Troo/And Bring Back an It-Kutch, a Preep, and a Proo,/A Nerkle, a Nerd, and a Seersucker too!"