@Frances, I can believe that! The book talks about how Tolkien's experiences made their way into his writing. The Dead Marshes being one of them for sure. The book also suggests that the four hobbits (especially Frodo) were a representation of how soldiers dealt with their time at war after it was over. Pippin and Merry moved on and turned their negative experiences into positive things, Sam moved on as if nothing happened, while Frodo could never move on and was haunted by what he experienced.