I kind of wanted to remind myself this idea constantly, so I was studying it from some of the animation clips on youtube.
He is trying to find the hole to slip into the jacket but it seems he couldnt find it once so he is fumbling a little bit. I guess there's a lot more to learn from this awesome shot but to me, this fumbling looks really great accent in timing.
The mouse is trying to escape from his hand but he stopped, I think this is one of the imperfection. And also he switched his hand left to right when he holds the mouse (I guess I shouldn't say imperfection but more like NOT simple efficient movement). At the last, the mouse it still trying to keep grabbing his shoulder and gives up.
Great Glen Keane's shot. After the boy blows his nose, he is still rubbing his nose. The mother missed to catch him when he jumps from the edge of the bed. Even before that, she seems not to realize the boy is climbing on there and shows her little surprise.The boy is trying to get out of the bed and moving around after he's caught by his mom. When she is trying to find his toy behind the pillow, she couldnt find it smoothly and look at how she moves left leg. Awesome.
All those little accent movement and acting are supposed to be decided by the situation, character and some more other elements. This gives not only variety of timing but also illusion of life.