I was just playing with our mixed breed Rosie. She had a new hard Nylabone that she'd brought over to me. As I was reaching for it, she shifted her hold on the bone and accidentally caught my third finger (kind of got snagged on a pre-molar). I yipped a bit and had my eyes closed, as it did hurt plus I wanted her to be more careful. When I did open my eyes, she was sitting there with her lower lip quivering. I could tell she was really upset as she was sitting very still, without a command, and staring. I reassured her but she still had the lip quiver for a minute or more.
My opinion is that she was upset about hurting the alpha dog in our pack. I got up and moved around, but when I came back and sat down, she followed me and tried to lick the fingers on both of my hands. She doesn't really do a lot of licking until we go to bed (seems like a social thing morning and night).
I did some reading on the forum regarding jaw quivering so wondered if anyone had more info or opinions. Thanks!