One of my cats has a default "worried" expression, like I'm not going to rub her head this time or I'm going to do something strange or suddenly get up and leave her. She has another couple expressions but the next one is a "crazy" expression :-) when she's had enough teasing (she's very easy to tease; I'm sorry, it's just fun trying to touch her feet without her nailing you first with her claws :-) where you know you're in serious trouble but just can't take something so small, soft, warm, and furry seriously? :-)