I want to describe the movement or position of an inner material inside an outer sheath, as the inner moves through the outer. Can anyone think of some kind of verb, spatial preposition or any other word or phrase?
For example, I'd like to describe the relative position of a cob of corn inside a bun, or the movement of a worm inside its tunnel.
In particular, I have something like an infinitely-long core of lego-bricks inside an infinitely long tube of different-sized lego-bricks, and I want to talk about the movement of the core along the tube. I can't talk about the absolute position, as there's no end-points to compare to, so I have to refer only to the relative positions of the bricks themselves.
Thanks for any help.