Humans always have changes in their facial expression when lying. Especially when they answer something in a way that is opposite from the way they actually feel. You can notice this especially in their facial expression. Their eyes can be relaxed when everything is indeed fine. But if they're sad they will look sad easier when you ask how they are, because the real answer is that they are not fine because of a certain reason

If something even happened they are ashamed about, they may look away in shame

If something happened they are angry about, they will have anger in their pupils

No matter how durable it looks, it will rub off!!! then you can’t tell your 1/3 from your 1/2 and your 3/4 from your cup in a dark cupboard!