
Experienced munis, those who are liberated souls, those who are expert in Vedic knowledge, they understand an avatara, or incarnation, by the symptoms, as they are stated in the scriptures. In the scripture, the color, the activities, the time and the place and the parents -- everything is described about the incarnation. Just like a drug is tested in the laboratory and the drug, the symptoms and the taste, how it is, how the color changes, how it tastes in the tongue, everything is described there, so a scientist proves, understands the genuineness of a particular chemical by testing. Similarly, nobody should be accepted as incarnation just like that. That is foolishness. Incarnations are stated in the scriptures. Their symptoms, everything is there, and one should understand from that. The avatara never advertises. Anyone who advertises himself that "I am incarnation," he should be at once rejected.
Ref: Srila Prabhupada's Lecture, December 28, 1966