Several times during the episode, the mouth of Doom's mask moves as he speaks.
Somehow Ben is able to spit on his hands through his space helmet.
Doom claims that he couldn't have stolen the Silver Surfer's powers in Earth's atmosphere, but he does just that in "Doomsday".
Silver Surfer: This is not the galaxy-spanning sphere of Galactus.
Ben: Well, maybe he's got a brother Irving, and this is his jalopy!