I`m sure most of you will have seen this excellent film ..but theres one part of his brilliant escape that I cant work out ..
After his escape through his tunnel the warden of the prison visits his cell wracking his brains as to how he escaped - he picks up a chess piece and in anger throws it at the poster on the cell wall - the chess piece goes straight through the poster revealing the tunnel..

How the F*ck did he put the poster up on his wall from inside the tunnel?

answeres on a postcard please..