Out of This World (1987) : 3x15

Evie is tormented by a commercial jingle for a mouthwash company, while Donna rushes to prepare for her commercial on live TV. Throughout the day, the twins that appear in the ad show up to sing part of the jingle again and again as Evie is discussing her retainer with her friends. Evie is confused as to how they keep showing up, so she and Donna turn to Troy for help, and he concludes that the word "mouth" triggers the jingle, she also complains about her retainer so she takes them out, and puts them back in when they leave for the studio. Troy leaves a message saying that the twins appearances were caused by the material in her retainers. Donna then goes on TV for her commercial, but her nervousness causes the word "mouth" to be spoken and the twins to appear and interrupt her, causing her to rhyme the rest of the ad. Buzz then hires the twins to be part of his new commercials.