When we didn't have A/C we'd give them ice cubes to munch on. We'd also wet them down when we were home (they were definately not a big fan of that, but they liked it afterwards). When we went to work, we'd take an empty 2 liter bottle fill it with water and freeze it overnight and put that in their water bowl. Ice cubes didn't work because Hunter likes to play with them and splashed all the water out of the bowl trying to get to them. Not only was it a big mess to come home to on my kitchen floor, but defeated the purpose of giving them water!