Sierra spins an impeccably rhymed yarn about a last minute science-fair experiment gone fabulously amok. As a bespectacled girl narrates, her classmates’ projects go swimmingly while she’s blocked: “The ants on Mary’s ant farm were growing corn and peas, / And Kevin Fink was on the brink of curing a disease.” Surfing the Internet, she sends for “Professor Swami’s Super Slime,” (“A mutant yeast with just a piece of dragon DNA,”) that arrives in an oozing carton plastered with warnings. Naturally, the stuff morphs. Sensitized to the slightest rebuff, it swallows the hissing Sir Scratchalot, kid sister Kate and Dad before chasing the narrator to school. It ingests Miss Fidget and several third-graders before the budding scientist remembers a crucial detail: fed sugar, the slime will swell amazingly, then erupt into a harmless gas. The kids lob a barrage of treats into the gaping maw, with—apparently—the guaranteed results. Gammell’s pictures perfectly capture the antics, exploiting runny watercolor and highly rendered colored pencil to depict the outrageous mutations. Explosively funny. (Picture book. 5-8)