I am not a fan of Marcus screaming about how they could donate bone marrow . In my opinion , they should have structured the story such that the Mountain Men needed something that can ' t be donated , to avoid the question of why they didn ' t just cut a deal Jasper , donate bone marrow every five weeks and stay out of trouble . In exchange , all the chocolate cake you can eat and whatever you and Maya decide to do in your off hours is your business . . . . Or give the skykids a weakness such that they actually can ' t donate bone marrow non fatally . Or just make it so the technique to do it safely has been lost to time . Something . Marcus screaming about how they should just donate it nonfatally undermines the whole plot . On the other hand , maybe the inability to cut a deal when it absolutely should have been possible makes the whole situation more tragic .