Its the episode where Sharon is going to be in a Lena music video. When Lena is singing rags to riches you see she is only wearing one glass slipper. Then the "prince" dude puts a slipper on her other foot. After a few seconds there is a close up on her foot and the slipper is gone. When the family is sitting around the TV watching the video, you see it the slipper vanish again.