We don’t worry about getting mugged or murdered by Tweety. Hyper-Alert Eyes, which in human faces indicate a heightened state of mental activity (possibly pathologically heightened), with stylized characters are seen as eager or extra-aware; an expression of their personality, rather than a special, transitory state. Tweety strikes us not just as friendly (slight smile, raised eyebrows in greeting or attention), but as energetically friendly.
Unlike Tweety, the mass murderer’s slight smile doesn’t seem like a smile at all – the facial details that express a truly happy slight smile, like the angle of the arc or the position of the mouth corners, are not correct. But with Tweety and other stylized characters, our smile detection criteria are extremely forgiving: there is a huge library of arc shapes or open mouth shapes that get the message across (a subject for a future blog post).
In fact, many expressions that work well on a stylized character look terrifying, or absurd, on a human face. Animators are fortunate that we have such relaxed standards when it comes to stylized expressions, as their job would be nearly impossible if they had to satisfy the same strict criteria we apply to real humans with similar, but demented, expressions.