Continuity mistake: Set in the 1930s, Steve Martin is teaching a class of grade-schoolers in one scene. This would only be picked up by Canadians, but one of the many flags on the wall is the new (as of 1965) Canadian Flag - Red Maple Leaf with two red panels on either edge.
Factual error: The boxcars in the opening scene have bar codes, but the film is set in the 1930s.