Sometimes books are returned to us with some interesting extras (personal notes, pressed flowers), and sometimes the books themselves return in…interesting conditions.
The patron who returned this book said that her dog had become frightened during a thunderstorm and, in its distress, chewed the binding of her library book. The friend who accompanied the patron noted that animal glues (including rabbit) are sometimes used in book binding. Perhaps this attracted the dog to the book?
To learn all you ever wanted to know about book binding glues (and how to make them!), check out this page.