Rub a steel file with a flint in a dark room, and notice what pretty sparks you get.
在黑暗的房间中用钢锉在燧石上摩擦, 就能够看到漂亮的火花。
国家地理科普(视频版)
I'm just basically using a type of Steel file which is called a float, it's something you want to do like quickly and you want to just like get those points down to even out the chewing surface.