How he would pay it back can be stated clearly. Alternate translation: "must pay it back by giving him a live animal" (See: [[rc://en/ta/man/translate/figs-explicit]])
This is an idiom that means that one life would replace the other. Alternate translation: "one life to replace the other life" or "to replace the one that he killed" (See: [[rc://en/ta/man/translate/figs-idiom]])