When Daffy descends into the subway, he disappears instead of appearing in the windows of the roofed entrance, because that is part of the painted background.
When Daffy catches Porky at the mailbox and is shackling him, Daffy says, "Wait 'til J. Edgar Whosis hears about this." - an indirect reference to J. Edgar Hoover. However, the closed captioning for this actually specifies 'Hoover', not 'Whosis'.