Isn't there something along the lines of "eliminate all the impossible options, and whatever remains however improbable must be the truth"?
So:
It is impossible that kava is composed of solar plasma.
It is impossible that kava is made out of a man-made element such as plutonium.
It is impossible that kava is made out of plastic.
It is impossible that kava is people.
It is impossible that kava is made out of neutron star material.
Therefore, kava is a mammal (but not human)