Thanks for the input!

I have a small bowl of water I microwave for a minute (or less, I check on it every 30 seconds), then add the rodents. I leave them in the water for an hour or so until they are completely defrosted. Then I put them on a heat pad and check them every few minutes. It usually takes three hours or so for them to warm up, but I do check them regularly, so they're not cooked or overheated.

I think I'll call the Gourmet Rodent and ask for replacements. I may have been given old products.