When you go to feed, DON'T stun the rat. If you do it improperly and it wakes up at an inopportune time, it will be very afraid and dangerous. Either prekill it, or put it in the cage alive and unharmed. Although there is a risk with live prey, it could also help entice him to get into hunting mode. Oh, and make sure you step out of sight so your boy isn't more concerned about the giants watching him than his meal. Good luck!