sick (cold)
So what are they? They're buttonhole scissors, used to cut open a buttonhole after you've sewn the stitches to keep the edges and ends of the hole from fraying. The screw can be adjusted to cut exactly the length of the buttonhole (which you practice on a piece of scrap fabric first, it's not marked) and by cutting the exact length, you have much less chance of accidentally cutting into the securing buttonhole threads and weakening or ruining the buttonhole.
Several of the public domain sewing books digitized in the Vintage Sewing Reference Library refer to the use of buttonhole scissors and the 1926 New Way Course in Fashionable Clothes lists them as one of three pairs of scissors every sewer should own (the others are a pair of shears and a pair of small scissors).
