Make sure that the snake has ALWAYS a dry spot in the terrarium.
Otherwise you can get skin-problems.
I wouldn't worry to much about it when the snake eats and reacts normally. Often such things dissapear after a while.
The suggestion of a tub big enough for the snake is a golden one!
Boa's like to bath and when you are lucky it will put it faeces in it. Keeps your terrarium clean!