get the blood of a stone有表达一事是不可能的意思.比如：It's no use asking you father for a loan.You can't get blood out of a stone.
向你父亲借债是徒劳的,你休想从吝啬鬼手里要到钱.
又如：They can't get blood out of a stone because I just haven't got the money.
他们不可能从石头里榨出油来,因为我没有那么多钱.
当然这个句子还可以看出一点.我们可以说get water out of a stone.石头中可不能冒出水来.如：He got his information out of an encyclopedia.You can't get water out of a stone.
他从百科全书中查到了资料.石头中可不能冒出水