I know a monster with two big horns. . . and a long tail. . . and big sharp teeth. . . ."" Kooky-looking children sitting in a circle frame the monster that emerges, bit by bit, as page by page they conjure up his features. As they endow the monster with more and more terrible qualities the children themselves become shakier with fright--but, just as he seems to be out of control, one of the kids gives him the magic power to change into a. . . (tension, while page turns) ""cockroach. And I stepped on him."" The book's small two-color pages are unprepossessing, but Myers' offbeat humor rates a second glance. And the small idea builds nicely, right to the ingenious end.