Hmm. RF power density in free space is a function of V/m: W/m^2 = (V/m)^2 / 377. The constant at the end is the impedance of free space. If you wish to compute the power absorbed by a rat you'd need to know its impedance, or perhaps the impedance of some specific organ.
That's probably a tough thing to calculate in a definitive manner given the number of conceivable variables. And does it add anything to the conclusion? All rats are likely to impede about the same at some frequency, so whatever the answer is it's effectively a constant; one that a rat can't do much about while remaining a conventional rat. Why not simply rely on the easily measured/reproduced V/m and assume that all such rats are experiencing the same power flux?
