Other mistake: When Travis shoots Yeller, his gun (a .50 Cal black powder rifle) doesn't kick at all. Ordinarily a gun of this type kicks hard enough to leave a bruise.
Old Yeller (1957)
1 other mistake - chronological order
Directed by: Robert Stevenson
Starring: Chuck Connors, Dorothy McGuire, Tommy Kirk, Fess Parker, Jeff York
Deliberate mistake: At the beginning of the movie Mr. Coates tells his wife that he will be gone "all of three months, maybe four." The first time we see Bud and Elizabeth Searcy she tells Travis that her dog is pregnant and that Old Yeller is the father. We then see her dog that does not look very pregnant. The next time we see Elizabeth she presents Travis with one of the pups. The problem is that the pup that was supposedly just born is about 4 months old.
Jim Coates: Now and then, for no good reason a man can figure out, life will just haul off and knock him flat.
Trivia: Travis, Ollis, and their mother all starred together in Swiss Family Robinson also. (Travis as Ernst, Ollis as Francis, and the mother as the mother).