Sentence:  Cows were kept in backyard barns , boys were hired to drive them to and from the pasture on the edge of town , and familiar to the ear , morning and evening , were the boys ' coaxing voices , the <WSD>thud</WSD> of hooves , and the thwack of a stick on cowhide . 
Meaning of the word marked with <WSD> tags:  a heavy dull sound (as made by impact of heavy objects)