“Sometimes miniature electric train cars simply will not stay coupled. At some crucial tunnel, curve, or grade, the locomotive charges forward, leaving uncoupled cars behind and possibly derailed. It often seems that extra exertion at switches, curves, and grades has something to do with the uncoupling.
“Much, perhaps most, of the film footage that you project is coupled into “trains.” Like those miniature trains, films must stay coupled and on track through something like tunnels, curves, and grades, and switches. Therefore, couplings—let’s, of course, call them splices or joins—are crucial. Making good splices is one of your key responsibilities as a film handler. ”
— The Kodak Book of Film Care, 1st Edition, 1983