“Mom?” “Yes.” “Nothing.”

“What is it, baby?” “Well, it’s just that wouldn’t it be great if mattresses had spaces for your arm, so that when you rolled onto your side, you could fit just right?” “That would be nice.” “And good for your back, probably, because it would let your spine be straight, which I know is important.” “That is important.” “Also, it would make snuggling easier. You know how that arm constantly gets in the way?” “I do.” “And making snuggling easier is important.” “Very.”

– Extremely Loud & Incredibly Close

This, of course, is drawn out in xkcd.