If you have a lamp heat up the rats head, then dangle it in front of him with tongs. That might help. Also prescent before giving it to him. I take it out of the fridge, put it under running hot water for 30 mins. Then I let it dry for few mins if its wet, take it out of the bag and place it under the lamp (mainly the head). This little trick will both prescent the tank + heat up the head and keep the mouse/rat warm. Usually my bp gets so excited that he strikes few times at the F/T laying on the screen above him.