Others will have better advice, but to start with, you shouldn't thaw the rat in hot water. Either thaw it in cold water, or put it in the fridge until it's thawed, then warm it up just before feeding. The rodent needs to be completely thawed, but thawing it in hot water can cause the tissue to start decomposing - the same reason you don't thaw frozen meat for human consumption in hot water. Even if you can't smell the rotten meat, your snake can, and usually won't eat it. When it's fully thawed and warmed up to a 'life-like' temperature, shake the rat slowly where the snake can see, using a pair of tongs so you don't accidentally get bitten, to trick the snake into thinking it's still alive. With snakes that hunt by scent, such as kingsnakes, you can just set the thawed rodent inside the cage and they'll find it, but with heat-sensing snakes like ball pythons they need movement as well as warmth so they think they're seeing something that's still alive, especially with a rodent that's been frozen.