Continuity mistake: When we first see the auditions at the radio station, there is a window which has "Gong Broadcasting" on it. Later on in the short, the wording on the window changes to back to front.
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.
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.