Back in the days when I was growing up and learning to sew (in the '50s) and our shoes had leather soles, Mom and I would put out needles on the worn part of the threshold between rooms. Then we would rub the soles of our shoes over the needle and we could use them awhile longer. I'm not sure that sharpened them or just got rid of the "rust" from our sweat when using them. Our house was built in 1918 by my grandfather and the thresholds covered the gap where the floor boards met in doorways. We put the needles on the part where the varnish was worn away, otherwise it didn't "work."