The Cat in the Hat Knows a Lot About That! has 40 half-hour episodes. PBS Kids renewed it for a second season of 20 episodes which premiered on September 10, 2012. A 20 episode third season is currently in development. Each episode features The Cat in the Hat (voiced by Martin Short), who leads neighbours Nick and Sally, the Fish, and Thing One and Thing Two on a variety of adventures in his "Thinga-ma-jigger", a Seussian contraption that can sprout wings, pontoons, booster rockets, change size, and do just about anything else necessary to further the adventure. The adventures are prompted by a question posed by either Nick or Sally
The Cat in the Hat read, and Spaulding provided Geisel with a similar list. Geisel later told biographers Judith and Neil Morgan that Spaulding had supplied him with a list of 348 words that every six-year-old should know and insisted that the book's vocabulary be limited to 225 words. However, according to Philip Nel, Geisel gave varying numbers in interviews from 1964 to 1969. He variously claimed that he could use between 200 and 250 words from a list of between 300 and 400; the finished book contains 236 different words. Geisel gave varying accounts of how he conceived of "The Cat in the Hat".