The Mattress Rugrats : Season 4 Episode 22

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.