I'm not certain what your question is, but if you're wondering where the phrase came from it was Shakespeare's play 'The Merchant of Venice'. In that, the merchant, Antonio, pledged a pound of flesh to the Jewish moneylender, Shylock. Sadly, he couldn't redeem the pledge and was about to have the flesh carved from his living body. Then Portia, the clever lawyer-lady stepped in and pointed out that he was not entitled to any blood, as that wasn't in the deal. Saved the day! Now we use the phrase in situations where people demand all that you have promised.