"Plan B" is part of the program
Little kids like to ramble and tell their own "stories" or ask questions in the middle of things. That's okay and a good thing. Let yourself be taken on the mind trip and dive into the conversation with your child. At some point, you'll come back to the story from the book.
Lively Stories Make You Want More
The bear may be read grumpily, while the mouse gets a squeaky voice. Depending on the mood you want to create, you can sometimes read in a whisper or extra loud. You can make faces, roll your eyes and gesticulate wildly. Try out what suits you and the story. You'll find out how much fun you'll both have doing it!