What does that mean ?
My guess is smoothing down cartridges anywhere there might be any rough edges and/or extra plastic residue that shouldn't be there but is leftover from manufacturing and molding process.
Close but no cigar. There's a little imperfection in the metal mold used to manufacture the casings. This imperfection translates into a tiny bit of plastic in every cart shell that needs to be removed (with my trusty Dremel rotary tool) otherwise the PCB doesn't sit completely flat inside the shell.
The job itself does't take very long, but afterwards I have to clean the casings under running water, and leave them to dry for 24 hours. Somewhat tedious, but it's not too bad.