Continuity mistake: When Sylvester and the dog are fighting in the cage, Tweety rushes out of the door to see them and he is initially standing well away from the door mat, but in the next shot he has moved a few inches back.
Continuity mistake: When Sylvester (dressed as a cleaner) sneaks up on Tweety's cage to capture the bird, he puts his dustpan and brush next to the cage. But when we see Tweety standing next to the cage, the dustpan and brush have gone.
Continuity mistake: When Tweety puts his blue hat on the tin of alum, Sylvester takes the tin and eats it including the hat. But when Sylvester is trying to capture Tweety by sucking him with a straw, Tweety is wearing his blue hat again.
When Sylvester cannot put Tweety Pie in his mouth due to him swallowing the alum, he puts Tweety back in the cupboard. When he does so, you can see a small can with "Friz" behind him - a reference to the director Friz Freleng.