Context: In 2025, a corporation called The Union has perfected the creation of artificial organs, which have replaced organ transplants. A potential customer can apply for an organ, which is sold on credit, at high interest. If a customer is unable to maintain payments, after three months, a repo-man is sent after the customer to 'reclaim' Union property. The process of the repossession is bloody & brutal, and often results in the death of the customer.Remy is one of the Union's top repo-men, who partners with his childhood friend, Jake, to collect on past due accounts. Remy is highly regarded within The Union as their top performer, though his occupation causes problems with his wife, who sees it as unsavory. After she leaves Remy when Jake commits a repossession in front of their home, Remy decides to transfer to a sales job, much to Jake's chagrin.As his final repossession job, Remy is sent to the residence of a music producer, whose work he happens to admire. After allowing the man enough time to complete a song, Remy prepares to repossess his heart. When he attempts to use a heart defibrillator to stop the unit, the defibrillator malfunctions, sending a large electrical shock through his body and knocking him into a coma. When Remy awakens from his coma, he is informed by Jake and Frank, his co-workers, that the shock severely damaged his heart. He can be fitted with an artificial heart, or die. After Remy attempts to flee the hospital, he reluctantly agrees to the procedure.Remy goes back to work, but is unable to perform his job, because he is just like the people he is repossessing from. He attempts to transition into sales, but quickly finds himself behind in payments. Jake takes Remy to the outskirts of the city to a nest, which is a collection of people who have past due accounts with the Union, but are fleeing to avoid being repossessed. Remy is again unable to perform a repossession, after which he is abandoned by Jake until he can perform his job. Remy is attacked by a pair of men from whom he was expected to repossess artiforgs, and knocked out.Remy, upon awakening, encounters Beth, whom he had met earlier in a bar where she was singing. He discovers that she has multiple body parts on which she is past due, and is currently suffering from a drug addiction. Remy takes her to a motel room, where he stays with her as she goes through withdrawal. After Jake interrupts his attempt to falsify artiforg returns on both of them back at the Union's headquarters, Remy leaves unassailed by Jake, returns to Beth, & the two leave to live in the outskirts.The pair live, for a time, in relative harmony. Remy uses an old typewriter that Beth has found to type up a narrative of his life, and subsequent conversion. As he finishes, a repo-man arrives to repossess his heart, but as he approaches Remy, he falls through a hole Remy has covered in the damaged floor, crashing to the floor below, unconscious. Then Beth, who was hiding behind the door, also falls when the floor collapses under her, re-injuring her leg. From above, Remy sees the Repo man coming to, readying to tranquilize or taze Beth. Remy drops the heavy typewriter onto him through the floor, crushing his head, to save himself and Beth. Using the repo-man's vehicle, Remy sneaks back into his former workplace to obtain a pair of devices that fool organ scanners used by repo-men. He attempts to force Frank to clear his account, only to discover that due to his previous aborted attempt, all accounts can now only be cleared back at the Union's central office.Remy and Beth attempt to flee the country at the airport, but are taken by security when it is discovered that Beth's prosthetic knee was damaged in their earlier encounter with the repo-man. Once inside, they are forced to fight against airport security and another pair of repo-men. They are able to kill or incapacitate 
 Question: What prosthetic body part does Beth have?
Output: knee