Sentence:  Instead , he constantly became lost in parts and components of them , confused some of their details with those of neighboring objects , and so on , unless he allowed time to `` trace '' the object in question through minute movements of the <WSD>head</WSD> and hands and in this way to discover its contours . 
Meaning of the word marked with <WSD> tags:  the upper part of the human body or the front part of the body in animals; contains the face and brains