What does the lump look like?
I would suggest getting a form of cooling device for the rat if ac isn't an optino. Like said above fans and frozen water bottles work well I also use to use mini containers filled with water and a rock. So they could lay in water to cool off if needed but have a way out without risk of injury. Make sure its only deep enough to sit in comfortably without having to swim or stuggle to keep theuir head above water. or getting really soaked. Just a shalow amout will do.
I would suggest getting a form of cooling device for the rat if ac isn't an optino. Like said above fans and frozen water bottles work well I also use to use mini containers filled with water and a rock. So they could lay in water to cool off if needed but have a way out without risk of injury. Make sure its only deep enough to sit in comfortably without having to swim or stuggle to keep theuir head above water. or getting really soaked. Just a shalow amout will do.