I don't necessarily believe what the mushroom tells me; rather we have a dialogue. It is a very strange person and has many bizarre opinions. I entertain it the way I would any eccentric friend. I say, "Well, so that's what you think." When the mushroom began saying it was an extraterrestrial, I felt that I was placed in the dilemma of a child who wishes to destroy a radio to see if there are little people inside. I couldn't figure out whether the mushroom is the alien or the mushroom is some kind of technological artifact allowing me to hear the alien when the alien is actually light-years aways, using some kind of Bell nonlocality principle to communicate.
The mushroom states its own position very clearly. It says, "I require the nervous system of a mammal. Do you have one handy?"
In, Tryptamine Hallucinogens and Consciousness, by Terence McKenna