Piggie teaches her pachyderm pal to pretend. Considering that this is their 20th outing, Elephant seems a little slow on the uptake, but he sees the light eventually. Hopping around her bewildered buddy with many a "Ribbet!" Piggie explains, "I was a pig. Now I am a frog." Gerald the elephant panics, thinking that he too might be transformed at any moment; there's all that hopping, and as for eating flies-! Piggie goes on to explain just what "pretending" is all about. Stunned-"And you can just do that?!" -and assured that even grown-ups pretend, Elephant resists Piggie's invitation to join her in the game. A characteristically hilarious spread depicts the two in heated debate, Piggie's seven pink speech balloons ("Yes you can!") tangling with Elephant's eight gray ones ("No, I can't!"). But he's got the last laugh, going on to let out a mighty "MOOOOOOOOOOOO!" Cue the animal concert. As ever, Willems gives figures drawn with elemental simplicity and broadly expressed reactions just a few, but often very large, dialogue words to tell the tale. Children aren't likely to need the instruction, but the validation may be helpful to counter imagination-repressing parents or older sibs. (Early reader. 4-8) Kirkus"