The shuttle metaphor is taken from weaving, of course: the shuttle is a block of wood thrown back and forth on the loom, carrying the weft or cross-thread between the separated threads of the warp. This metaphor may make the translation process seem mechanical, like throwing a block of wood back and forth – and clearly, it is not. It may also make it seem as if the two states were totally different, perfect opposites, like the left and right side of a loom. The two states are different, but not perfectly or totally so.