Grandpa is suffering from aches and pains all over his body. The cause of all his suffering -- his mattress, which he was sleeping on since World War II; he was sleeping in it for so long, he has left his body-shaped indentation on the mattress. Stu forces Grandpa to give it up by throwing the old mattress into the trash and buy a state-of-the-art bed in its place. While Stu throws the mattress away, the Rugrats look on, thinking that it was the monster that caused Grandpa to writhe in pain so much. (thetvdb.com)