In our terms the trace is any enduring mark left in or on a solid surface by a continuous movement. Most traces are of one or other of two kinds: additive and reductive. Additive traces can be produced by means of a range of manual implements that deliver a material pigment to the surface, including pens and brushes. Unless scratch marks are the ultimate cause of fracture, cracks show no respect for the traces that may have been drawn over a surface. Thus cracks interrupt traces rather as, in the landscape; a path of travel may be interrupted by a precipitous gorge in an otherwise level plateau. Like threads, traces abound in the non-human world. A thread is a filament of some kind, which may be entangled with other threads or suspended between points in three-dimensional space. At a relatively microscopic level threads have surfaces; however, they are not drawn on surfaces.