I have no idea if Kage Kara Mamoru is drawn on cels or if it's all digital...but either way it's funny the little things you notice (especially if during a slow workday you're watching anime). In the OP around 1:18 Yuuna's running with slice of bread in her mouth--in episodes 1 and 2 her mouth's partially open and it has white fill, which I remember thinking was a little odd looking (is the inside of her mouth glowing?):
But sure enough, by episode 4 her mouth's closed and the white fill's gone:
I always think of Animation Runner Kuromi when I see little changes like this and wonder if on the other side of the Pacific there's a director who's noticing these things and cringing when the first episode airs, but the schedule was so rushed there was no time to fix them. In any case, I salute the people who take the time to go back and fix the little things in anime--it's probably not something a lot of people notice, but when you add it all up it makes a difference. Although it's not like Kage Kara Mamoru has the slickest animation I've ever seen, so maybe I picked a bad example.