Congrats on the new snake! As far as the "marks" you can see, it wouldn't hurt to contact the breeder since you are friends and just ask. It's likely just internal organs but heck, it never hurts to ask the breeder and you'll likely get a very interesting internal structure of your snake kind of lesson.

Colubrids like your corn, really any young snake, are nervous. When you're small enough to be somebody's dinner, well heck - it must be a bit nerve wracking LOL. Their instinctive need to survive makes them tend to be jumpy, makes them nip sometimes or just jab at you (a close mouthed defensive smack like your snake did to you). Some colubrids will also use musking when they are stressed. That really, really stinks - quite amazing a small snake like that can make such a nasty smell LOL.

Like any snake species, you want to make sure your care of it is bang on (housing, temps, hides, etc.) and then leave it be to settle in for a week or so. Then offer it whatever it's been eating at the breeder's home in the same manner it's been fed so it knows that is dinner and it's dinnertime now. Routine works with snakes and some get very put off if their routine changes drastically. Once the little snake has taken some meals, then work on calm handling for short time periods.

Colubrids like cornsnakes (we have a milksnake but they are very similar in a lot of ways) are escape artists. You must have a super secure lid on your enclosure or they will escape. You must keep them in hand at all times or they will end up inside your couch faster than you can blink. They generally are busy, inquisitive, fast moving snakes so handling them is a lot different than your average ball python. BP's are ambush predators, cornsnakes and the like are active predators so that affects how they treat their world and how you interact/handle them. '

Enjoy your new corn! Can't wait to see pics of it.