Talmud Sanhedrin page 61a.
We have a outside teaching--(a braita) that says we know you can't serve idols in a way that is not usual from the verse "He who sacrifices to the gods will be destroyed."[Exodus 22] Rava asks: "Why not learn this from "He will bow?"[Deuteronomy 17]
Rav Acha asks on this question of Rava thus: If we would learn from "bowing" then what would "How do they serve?" ([Deuteronomy 12) come to tell us?
Tosphot asks on this question of Rav Acha why did he not ask it on the the original Braita where we learn from "sacrifice?"
The Gemara in Sanhedrin page 61a and the second Topshot that starts, "How do they serve?"
Idolatry should not be worshiped in one of two ways. One is its normal service and the other is not its normal service. The not normal service in order to be liable needs to be either sacrifice, burning, pouring, or bowing. If one just hugs it, then he is not liable (if that is not the usual way of worship).
But the idea of the normal way of worship is a bit frightening. What if someone says, "Give me charity, and I promise you a good year?" Is that idolatry if someone gives him money? It certainly seems so. After all it seems the basic implication is that the person involved is claiming Divine powers. And that seems to be all one needs in order to be considered an idol.