Need help on switching from mice to rats.

My BP has ate four mice with no problems. Two weeks I tried to give him a rat pup but he didn't even look at it. I left him alone for a week then tried again last night and no luck. He is acting a lot different the the rat pups than he does with the mice. He goes after the mice right away. With the rats, it's almost like he is going up to them to smell them. I have put the rat in mice a bedding overnight to try and get the smell on the rat but no luck. Any idead on what I can do now?

You're feeding live, I gather? Try doing the rat pup in the mouse enclosure again, maybe for two days, and then also place some soiled mouse bedding in the snake's enclosure for maybe half an hour before you feed him.

If you want to be even more thorough, do the above and leave a mouse in a cage right near the snake's enclosure. Then drop in the rat pup and see if you can fool him into thinking it's a mouse until he grabs it.