How script supervisors keep film continuity - and coffee cups and cigarettes - in check

[Extract] You’ve seen the Game of Thrones scene with Jon and Daenerys where somehow a Starbucks coffee cup made it into the frame? Or maybe the one in Star Wars where the Stormtrooper misjudges the height of a Death Star doorway and, unnoticed by anyone else, smashes their head?

You may have even noticed bullet holes on the walls before anyone started firing at Jules and Vincent in the apartment scene from Pulp Fiction.

Those moments might have ruined the scenes for you - or perhaps were the only redeeming feature. But the big question everyone wants answered is: whose fault was it?