I have been thawing the rats in the fridge. I put move them from the freezer to the fridge the night before. When I am ready to feed him the next evening I just take them and put them in a sink full of water as hot as the tap goes (in the ziploc bag of course). After they feel reasonably warm I blow dry them while focusing on the head to increase the heat signature. I haven't had any problems with them popping. I was trying to thaw them from frozen when I was ready to feed him before and was just always concerned that they were either too hot or not fully thawed. The fridge has been working great since I know they are not frozen by the time I warm them and I don't have to use very hot water to bring them to temperature. Have you only had the problem with the rat popping once or is it a regular thing? It could have just been an isolated event, but incorrect thawing can cause that too.