The 3rd image looks like it's 'bruised' itself a little, likely from squeezing in to a very tight spot, which Boas just *love* to do. I wouldn't worry about it too much, it'll probably throw itself into a moult to repair the damage.
When you see loose skin on a snake like in the 2nd image, it's usually a sign that the skin is growing faster than the body it covers. I know it sounds strange, but I've seen it many times and upping the food intake usually solves that rapidly. Just a thought