Great App but... – Dr. Seuss Treasury Kids Books Review

I got this app so that my 6 year old granddaughter could practice reading. She was reading mr brown on this app and she kept saying the word sound instead of go and she told me that in the book ( board book) the word is sound not go. Can you please explain why the words are changed and the book is longer in the app?
Review by Nanny166 on Dr. Seuss Treasury Kids Books.