Grandma's Kisses / Squidville - S2-E9
Other mistake: Grandma's Kisses: After Grandma pulls the plug from the floor, she kisses SpongeBob and says that he can kiss his Grandma and still be an adult. In this shot, SpongeBob's legs are completely missing. His pant legs also vanish and reappear mid-shot, and even his legs appear for a frame or two, then vanish. (00:11:48)