In terms of the Talmud in Sanhedrin page 61a I want here to state what I think is a major question.

It is the question of Rav Acha from Diphti on Rava. His question is if Rava would be right then what does how do they serve come to tell us. Now at first it looked to me like he could even skip this part of his argument and go right to his question--the contradiction between Rabbi Elazar and Rava. But this I realized afterwards was wrong. He needed to lead up to his question because he wanted to make sure that bowing would be placed in the area of service not according to the way of that idol. And then he could ask the question from the statement of Rabbi Elazar.

But then my learning partner asked, "Why does he not ask straight from Rabbi Elazar onto the original Braita?" 
Now at first I thought that that was the question of Tosphot but it turned out that that is not true. Tosphot asks something that superficially looks like the question of my learning partner but is not in fact the same. Topshot ask if the question from "How do they serve?" (Deuteronomy 12) is valid for "bowing" (Deuteronomy 17) why is it not also a question on "sacrifice" (Exodus 22)? And that is relevant only to that stage of the argument. The question from my learning partner is totally different. It is not Rabbi Elazar starting with a completely different set of assumptions from the Braita? So why not ask straight out from the beginning: "Do we learn serve not according to the normal way from "he who sacrifices to false gods will be destroyed"(Exodus 22) or do we learn from "So they shall no longer sacrifice to the goats."(Leviticus)

Just for reference for those who do not have the Talmud Sanhedrin in front of them here is the basic idea:

Braita: serve to an idols according to the non-normal way of that idol is forbidden because of  "he who sacrifices to idols will be destroyed"

Rava: why not learn from "he will go and bow"?
Rav Acaha: If Rava would be right that we could ask from bowing then what would we do with he how do they serve? It has to be for dishonorable service. But then what would we do with Rabbi Elazar who says, "We know one can't sacrifice to Mercury because of the verse 'so they shall no longer sacrifice to goats.'"