DS has recently started putting his head back to see what's behind him when he's lying down. He also twists his head round quite far if he's sitting up, again to see what's there. MIL says this is a really bad thing to do, and if someone stands behind him (thereby making him look) she goes absolutely nuts, really shouting at them!
I looked it up and can't find much that says anything about it online, so I'm wondering whether is really true, or whether it's one of those old wives' tales (MIL LOVES an old wives' tale; always believes them).
Anyone know?