I was talking to someone with a lot of experience with these snakes and one thing that they mentioned, which I should've already mentioned, is if the snake's health is affected in any way you should see a veterinarian.
The one that I saw didn't appear to have any health problems, the lines didn't appear to affect its health. That's why I assumed the same for your's, which was wrong for me to do so. Please don't be offended by this, without pictures and/or actually seeing the snake, its best to safe than sorry.
Now then, on to some possiblities. The person I talked with in essence said that creases can become more defined or severe in overweight snakes and sometimes even in severely underweighted ones.
I suppose that its more of a stretching of the skin by body fat due to coiling. The lines usually remain for a period of time even though the snake's body is in a different position.
Unfortunately, overweight burmese pythons are very common. A lot of people think they're supposed to have really large diameter bodies. While they are a heavy body snake, they're not to be fat. This can greatly reduce their lifespan and cause other health problems. It can be hard for the average person to distinguish between an obese burmese python and a normal size one.
Take care!
Mike
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