First appearance of Sylvester Jr.
The circus background was done in a style similar to that seen in Disney's Dumbo, in 1941.
Hoppy (and his mother) looks more like a kangaroo here. Later on, he would become more of a caricature. Interestingly, although rodents and marsupials are from different branches of the mammal family, there is a slight facial structure resemblance to kangaroos and mice.
The curious looking object behind Sylvester that's seen when he's first talking to his son is an old fashioned home incinerator. Back in the day, folks simply burned their rubbish in such a structure. Escaping sparks were commonly seen when it was in use.