You gotta admire their inquisitiveness :-)
One of mine did that once with a kitchen roll tube. There was a little straining face one end and a pair of feet the other like something out of a Tom and Jerry cartoon.
It was a useful lesson in the sort of fixes ferrets can get themselves into. I'm careful to keep such things out of their way now. A cardboard is easy enough to tear open. Good job it wasn't plastic.