The Right to Bear Arms - S1.E5

Major Doctor Ghastly invents a new machine called the Cerebro-Ransmuter 2000, It can put Hector's brain into anyone's body, and Skarr becomes that body. But Boskov's arms end up onto Skarr's body, and Skarr's arms are put onto Boskov's. They both then discover that he is able to make his own arms move. Even on someone else's body.