Leave the pup in the enclosure and clear the room of humans next time. Also, don't remove the hides. As long as the rat is not yet weaned, it can't hurt the snake. If it's well furred and/or has opened eyes, then it is not to left in the enclosure unsupervised. Otherwise, you can leave it overnight if necessary. Sometimes the switch from mice to rats requires patience. If the snake refuses rats a couple of times, offer mice again. The most important thing is that the snake feeds.