Both segments were being produced independently as full length features, but when wartime shortages lost the studio resources, time and animators (who were drafted), Walt Disney made the decision to combine the two.
Edgar Bergen was one of the most popular ventriloquists of the 1940s even having his own radio show featuring Charlie McCarthy and Mortimer Snerd. After seeing this film he said he was dismayed to see how much he moved his lips, blaming it on the fact that on radio he did not have to not move his lips and had become spoiled.
This is one of the first Walt Disney films to list the voice credits for the animated characters, and the first to actually list Mickey Mouse, Donald Duck, and Goofy as if they were actors in a live-action film.
Mickey attempts to convince Willie to turn himself into a fly so that he can be swatted. In Brave Little Tailor (1938) Mickey killed seven flies with one blow and is sent on a quest to kill a giant (as everyone thought he was talking about killing seven giants).