Dog fight
Between Lassie and Satan. It looked fairly realistic. I'm also fairly sure it wasn't a real fight, since these dogs are somebodies property and even in 1943, there would have been a hue and cry over a real dog fight. But they did such a great job at editing, you really couldn't say for sure.
I read the book as a young boy but don't recall a fight with a sheep dog in it.
Democracy is the pathetic belief in the collective wisdom of individual ignorance. H.L. Mencken