Hope it's not a bill!

My son Caleb sometimes says the craziest things. Just yesterday he got a Thanksgiving card in the mail from Jen's parents. Jennifer told Caleb he had some mail and out of the blue Caleb says with all seriousness, "I sure hope it's not a bill!" Where did that come from? I didn't know four year olds had to worry about bills. I guess he may have heard that out of our mouths one time or another.