This is called 'the land of the free and the home of the brave'; it is called the 'asylum of the oppressed,' and some have been foolish enough to call it the 'Cradle of Liberty. ' If it is the 'Cradle of Liberty,' they have rocked the child to death.
You don't cast the animal, per se. You have an animal trainer who looks for several of them. That is a different experience than dealing with actors. That is just difficult. It is what you expect from an animal on the set. You just run a lot of film and prompt it to do the right thing, but sit through it doing all the wrong things first. It's just unbelievably boring, frustrating and painstaking to shoot.