Some sorts of door latches have a piece of string through a hole, that when pulled, lifts the latch within. Sometimes, to stop it being opened, the string is withdrawn through the hole. To help thread the sting back in the morning or whenever, the string is tied or spliced to a piece of metal, a spike or something known as a cotter pin. Sometimes this is stuck into the door outside, or through an eyelet. To open a door that has its string on a pin through the eyelet, you have to twist the pin, like winding a spindle, this twirls the string, the latch lifts and in you go.. I know this sounds complicated and obtuse, but it's how we used to open the shed door on my grandfathers' farm to let the cats out into the barn. The cats could jump to the latch and would quite often pull the string out, then play with it and break the latch, so Granfer spliced a pin to it, and stuck it in the door, so the cats couldn't pull it through...

LTS