Sentence:  This meant , concretely , that the patient could not read at all without making writing like movements of the head or body , became easily confused by `` hasher marks '' inserted between hand-written words and thus confused the mark for one of the letters , and could recognize a simple <WSD>straight</WSD> line or a curved one only by tracing it . 
Meaning of the word marked with <WSD> tags:  a line traced by a point traveling in a constant direction; a line of zero curvature