What does "pound of flesh" mean?

A debt whose payment is harshly insisted on, as in The other members of the cartel all want their pound of flesh from Brazil. This expression alludes to the scene in Shakespeare's The Merchant of Venice (4:1) where the moneylender Shylock demands the pound of flesh promised him in payment for a loan, and Portia responds that he may have it but without an ounce of blood (since blood was not promised). [c. 1600]