“A Dog’s Purpose” -- the upcoming major motion picture based on the best-selling novel by W. Bruce Cameron -- is set to open later this month, but new footage obtained by TMZ may give animal lovers pause about going to see it. The exclusive video shows an animal trainer forcing a terrified German shepherd dog into a pool of raging water, while the animal tries desperately to escape. It’s a chilling behind-the-scenes look at the filmmakers’ attempt to recreate a scene from the book, in which a police K-9 named Ellie rescues someone from a rushing river.