Book 4b of the Key Words with Peter and Jane reading scheme features Peter and Jane interacting with farm animals, introducing 41 new words like 'work', 'thanks', 'stop', and 'horses'. After finishing this book, the child proceeds to book 4c. The scheme gradually introduces and frequently repeats key words to help children recognize them on sight, using the 'look and say' method. Examples of key words include 'the', 'one', 'two', and 'he'.