Mark asks:

> Egad.  What's next; a water-cooled rat?

Actually, that's already been invented (about 250 million years ago, if not a
bit sooner). See:

    http://www.helsinki.fi/~jyhokkan/phd.htm

(just to make the reading a little easier, mammals & birds are endothermic
homeotherms; reptiles are ectothermic homeotherms).

Rodents coat their front legs, which are heavily vascularized and thus
represent an easy mechanism for the fluid transport of core body heat to the
skin surface, with saliva and let it evaporate in order to cool themselves
when they become overtemperature.

Although the author above talks primarily about large animals (mammals,
reptiles and dinosaurs), which are to a great degree de facto homeothermic
due to their large masses and must evolve mechanisms to lose the excess heat
of metabolism, the problem of thermoregulation is reversed in small mammals,
which by their very nature, have a large surface-to-body ratio and lose heat
too readily. As a consequence, a little bit of spit on the front legs goes a
long ways in cooling mice and rats.

Wirt Atmar