What ive done in the past is wash a rat,just with water and rub the rat with the mouse,once the snake smells the rat in which should smell like mouse,hopefully it will take it.Once it starts eating dont rub the rat as much with the mouse.In time your snake should take the rats.I had a Darwin that would only eat mice,tryed scenting with the mouse,no worrys.Now he eats,chicken necks,rats and mice,basically whatever is in front of him...