Shawshank is bolx:
So this guy has a huge poster, which covers the slightly less huge hole he has carved out, with a teaspoon, to the outside world via various pipes and sewers.
Connecting an airless prison cell to the windy atmosphere outside would surely make the poster flap a bit? Create a bit of a draft in a cell which should be draft-free? Suck the poster backwards and forwards a bit in a manner suggestive that the wall behind it was less than solid, to any guards who might have been inspecting the cell?
And as for sympathetic portrayals of lifers!
Howzabout Shawshank 2, starring Kenneth Noye? Or Harold Shipman? Or Fred and Rosemary West? Or Myra Hyndley and Ian Brady?