Continuity mistake: When we see "Ben Birdie" on the stage at the start of the cartoon, he is surrounded by a piano, tuba and a drum, but when a mouse appears out of the tuba in the next shot, the drum has completely disappeared.
Continuity mistake: When Owl Jolson is performing "I Love to Singa" at the radio station, his family peer through the window and you can see a violin in its case. But in the next shot, the violin is on the floor with the case nowhere in sight.
Continuity mistake: When Porky Pig falls asleep in his boat, he is wearing a red shirt. In his dream, a big fish cuts off the red shirt to cook a now naked Porky. When the dream ends and Porky wakes up back on his boat, his red shirt is still missing, and he's still naked. He should have still had his red shirt on.