Those finely barred feathers on the sparrowhawk's torso are simple and yet tricky to do at the same time. Like the grass in my kangaroo coaster, I need to make sure it doesn't end up looking like a uniform bunch of lines. The bars follow the contours of the feathers, which in turn follow the contours of the sparrowhawk's body shape. Some of them overlap, and some are ruffled to reveal the soft down between them. It's a simple pattern but it needs to be done right in order to look natural, and it's simplicity is what makes it so easy to get wrong!