The big concern here in our eyes is the revelation that Mr. Frisby kept an elaborate secret from Mrs. Frisby. This is explained as something that he had been earlier sworn to secrecy on. Parents should explain that this is obviously not a practice for a loving husband and wife, just as it is important for children to be completely open and honest with their parents. There are a couple of references that refer to evolution that can be a conversation starter. Also, while not what we would call 'concerns' a couple of the Christian external reviews below point to interesting topics that can be discussed.
