It’s a redrawn, forty-fifth anniversary edition of Sandra Boynton’s first book, originally published in 1977. I don’t have the original drawings to compare, but this one certainly captures the classic Boynton style, with simple, colorful illustrations, full of personality. It’s a rhyming, counting book, first counting forward and then back, as one hippo calls two, and then further (ever growing) groups arrive for a party, then depart the next day. It invites the reader into math, wondering just how many hippos did party together, and the final line of the book provides the answer.