1.) Usually long speeches start with some sort of formal introduction line to set the stage for the audience. Sinon’s speech (teh formal part of the speech, not his initial lament) simply starts. The transition is so jarring that line was added later to give the speech a more characteristic feel. But vergil knew what he was doing. The absence of the introductory line gives the speaker makes the speaker substanceless, as though he is a voice without a body or person behind it.
2.) The speech is a good illustration of how what does all the heavy lifting in manipulation is not intelligence but egoism and self-absorption. Sinon never ceases to speak about himself.
3.) The main rhetorical lever of the speech is Sinon’s tale of hardship, that is, the moral authority that we impute to people who have tales of sorrow. No one questions or disputes a doctrine or belief that one bases on, say, a dead child.
4.) The speech is heavy on pathos but light on coherence. What relation does Sinon have to Belidus? How could Sinon’s father both be poor and afford to send him in arms to war? Again, how does the poverty of his father jibe with his reference to having a kingdom? Who is Sinon’s friend that Odysseus kills? All the details are sad, to be sure, but they don’t form a coherent narrative.
5.) Sinon manages to display about half the characteristic features of a liar in the opening lines of his speech: he is over-formal, emphatic, answering questions no one is asking, protesting his honesty when no one questioned it, etc.