Continuity mistake: When Daffy sends the Martian an ultimatum, the ultimatum goes back into a bullet and lands on the floor of the Martian's spaceship. But when Daffy sends him an ultimatum saying "Ouch!" there is no sign of the bullet.
Continuity mistake: When Duck Dodgers claims Planet X with his flag, you can see there is nothing next to him, but when Marvin the Martian comes along and makes his claim, an "X" tree has suddenly appeared.