I place my rats in baggies to thaw for several hours. Then I put the baggie in a large bowl with the hottest tap water that will come out. (Don't boil water on the stove or in the microwave). I leave the baggie in the hot water for about 6 - 7 minutes for pups and weanlings, and for smalls to mediums I replace the hot water after the first time period for an extra five minutes or so. If the rat comes out of the baggie wet, I dry it with a paper towel followed by a shot under a hairdryer for a minute or so.

If it isn't warm enough, as you have seen, they will just look at the rat trying to figure out what it is. It's the heat, along with the smell, that triggers the strike.

Good luck!