Mickey Mouse went through a design change in this cartoon. His body became slimmer; his head, hands and feet became larger; his tail was omitted; and, most notably, his ears were hollowed out and reshaped to work in perspective. The new design lasted until after WWII.
Mickey wears his usual classic red shorts for the fourth to last time in "The Little Whirlwind" from 1941, the three other last ones, where he wears them are: the 1941 Mickey Mouse Cartoons: "Orphans' Benefit (1941)" and "Porgimi la zampa (1941)". The final Cartoon where Mickey wears his traditional red shorts is the 1943 Mickey Mouse Cartoon "Pluto E L'Armadillo (1943)". Mickey in his red shorts wouldn't be seen in Animation, until the 1988 TV film "Buon compleanno Topolino! (1988)" for Mickey's 60th Birthday Celebration in 1988, as well as his cameo appearance in "Chi ha incastrato Roger Rabbit (1988)" and again for the first time in a Mickey Mouse Cartoon in "Topolino e il cervello in fuga (1995)" from 1995.
This cartoon introduced new, unique designs for both Mickey and Minnie that were short-lived. These changes in the designs included a slimmer body, perspective ears and a bigger head, hands and feet as well as buck teeth (the latter lasting for just two shorts; the 1941 Mickey Mouse Cartoon "Una Talpa Dispettosa (1941)" was the other), but only shown when they're whistling. These designs would last until the 1946 Mickey Mouse Cartoon "Due scoiattoli dispettosi (1946)".
Storyboards for this cartoon have Mickey drawn with his older, more circular ears, as they were made before his design was updated for the finished film.