Pask, p.122, states, All jumping moves are compulsory. Every opportunity to jump must be taken. In the case where there are different jump sequences available, the player may chose which sequence to make, whether it results in the most pieces being taken or not. Hopper, p. 102 and Pike, p. 113 both mention the huff or blow. Hopper says it is obsolete. Pike says it has been abolished. The idea of the huff was that if a player refused to make an available jump, the opposing player could remove the piece that should have jumped. In modern checkers, all jumps must be taken. Reinfeld does not mention forced jumps in his rules, however, elsewhere in the book, p. 18, he makes it clear that In checkers, captures are compulsory. In American checkers, a jump must be made only over an adjacent piece. A piece cannot jump over empty squares. Although no one actually says so, it is strongly implied that single pieces cannot jump backwards.