At Leather's concert at Arnold's, when Fonzie and then Leather both address the crowd, they speak into the microphone. However, when Leather sings, she uses no microphone, and same neither do her backing singers.
At the end of the episode, when Ritchie and Jonie are leaving, they tell Al that they are going to turn out the lights. When Ritchie reaches for the switch, it is already off, the switch doesn't move, and the lights go off.