Sentence:  Ancient nomads, wishing to ward off the evening chill and enjoy a meal around a campfire, had to collect wood and then spend time and effort coaxing the heat of friction out from between sticks to kindle a flame. With more settled people, animals were <WSD>harnessed</WSD> to capstans or caged in treadmills to turn grist into meal. 
Meaning of the word marked with <WSD> tags:  To place a harness on something; to tie up or restrain.