Sentence:  I do n't know whether he was after our rider , who had gone by a minute before , or whether he was simply scouting conditions ; but when he passed us by , a musket roared , and he reared his horse , swung it around , and began to <WSD>whip</WSD> it back in the direction from which he had come . 
Meaning of the word marked with <WSD> tags:  beat severely with a whip or rod