I agree, the rat needs to be warmer. Thaw the rodent in water that is a bit above luke warm until the rat is soft and thawed all the way through. Then dry it well with a paper towel until it's dry and fluffy. Then dangle it in front of the snake. If the snake shows interest, hold it still. if the snake doesn't show much interest, make the rat "walk away from the snake slowly", this will sometimes trigger a strike. Balls are an ambush predator, so if you start dancing a cold rodent on top of the snake, the snake may ball up and be less likely to eat the f/t rodent.
Rick