All of my snakes always shed out in one complete piece each time. Well, last night my female normal shed out - it was all in one piece from the neck down - for some reason her head didn't shed very well. Why would this happen.

I helped her along with a damp washcloth and the majority of it came off but I am unsure about her eyecaps. This was the first problem with a shed I've experienced. The humidity in the tank was plenty high enough around 70%

Any thoughts on what happened or does this sort of thing just happen from time to time.

Thanks