:up: A similar-looking idiom, which doesn't mean the same thing, is used by adults when their children have forgotten something [again; typically]: '...You'd forget your head if it wasn't screwed on.' (Perhaps this is dying out; I heard it [not just applied to me] a lot when I was a child, but I think present-day parents say it less [possibly because the current way of thinking requires more respectful treatment of 'younger citizens'].
b