To echo what another poster already said, it's all about the nerves. Several years ago I tried to kill myself by cutting my neck. I sliced below the jaw-line

To echo what another poster already said, it's all about the nerves. Several years ago I tried to kill myself by cutting my neck. I sliced below the jaw-line from my ear to my chin. I still have "numb areas" after 3+ years, and there aren't really any muscles there that need to be controlled. It's very easy to imagine not ever getting full facial muscle control back in her situation.