Now, I'm not an exegete. I did take a look at a number of different translations, including some Portuguese translations, and I will say this: every one I saw used some form of the word "make" or "cause" in verses 29 and 30. Which is to say, it seems that whatever words Jesus actually used, the thrust of His comment can probably be safely summarized as "if a part of your body causes you to sin, get rid of it."
So, the first car on this train (and remember, once a train gets started, it's pretty hard to stop, so if your car stalls on the track, grab the baby from the backseat and run - don't spent those thirty seconds praying that God will refill your gas tank like He did the widow's jar of oil!) is my (perhaps not all that novel) interpretation that Jesus chose the word "cause" for the very reason that it invalidated right off the bat the idea that He intended anyone to self-mutilate. Jesus makes it pretty clear at other times that the fault for our sin lies at the feet of our idolatrous hearts (okay, terrible metaphor, sorry!), not at the doorstep (again, I apologize) of circumstances, other people, or our raging hormones. When Jesus says "if your eye causes you to sin," I suspect He intended to subtly remind us that our hands are NEVER the cause for our sin.
Okay, so if you'll grant that interpretation (or if you won't, but will agree that He didn't mean it literally, or even if you disagree entirely but are a masochist... or if you just really like trains?), move with me into the business class carriage. Here we find ourselves wondering, gosh, haven't there been people over the years who have actually sliced off parts of their bodies (guys, don't tell me you didn't have at least one moment of terror as a teenager over this verse) because they believed this was a literal commandment? Now, none of us would accuse Jesus of being careless with words, and yet... do we not generally consider that love for one's neighbor involves taking a reasonable amount of care that what we say will not give occasion for anyone else to be confused or to commit sin? How much more so if you are the Lord of the Universe, knowing full well the foolishness of humans, and even knowing the future itself, so that the effects your words will have are already written in your mind before you say them? You may argue that, no matter what He said, Jesus was bound to be misunderstood, and He could not simply remain silent on that account. But that is not a valid reductio ad absurdum - certain things Christ said cannot be misinterpreted but by the hardest of hearts, while others frankly beg for the budding convert to seize upon incorrectly, foolishly, and with greatest zeal.
Then what? On to the coach class, where most of us spend most of our time. Shall we agree with the Catholics that "the fuller sense of the Bible can be found in the authoritative interpretation of [the]... authorities" - i.e., that it best to check with the Church before coming to a final conclusion about what the Scriptures mean? This seems insufficient - the apostles and prophets, not to mention Jesus Himself, are recorded as speaking directly to the common people on a regular basis, and we should not assume that this was done merely as a convenience, or for the sake of 'the public record.' If not that, then what?
It certainly seems to me as though this passage can only be rightly interpreted in the light of the rest of Scripture (whereby we learn that our hearts are the issue, and that constantly reorienting ourselves - loving - our Creator is the only way to live a good and righteous life that is free from all sin). This is an ideal that gets bandied about a good deal these days within the circles in which I run (ha, take that, sneaky prepositions!), but I don't think we take it all that seriously, because it posits a frank impossibility that we're reluctant (or entirely unwilling) to acknowledge - namely, that no matter our wisdom, brilliance, learning, and love for God, we will never be 100% certain about what all of Scripture says, because to know any one part of it requires that you know all the other parts. This is, at the very least, an impossibility within a non-infinite lifetime (it's really a study in mathematical limits, if you think about it - and don't you go inventing a theological calculus!).
Also, because coach is usually cramped and longer than the other parts of the train, I want to come back to the question of how we use words. I have often thought that part of our imperfection was our inability to accurately gauge how our actions will end up affecting our world. That is, if I were wiser, more careful, etc., I would have known that using that particular word would cause someone to think my tone was negative, thus encouraging them to respond negatively, etc., etc., usually spiraling into rage and violence about whether or not D minor really is the saddest of all keys. This passage, however, seems to indicate otherwise. Jesus knew that some people would be foolish (I don't mean this pejoratively) enough to cut off body parts in order to keep His commandments, and though this isn't what He intended, and probably brought Him no pleasure at all despite their well-intentioned attempt to obey the letter of His law, He chose His words carefully, with nothing but love for His hearers (both present and throughout the ages). And yet, it was not His intent to somehow choose His words in a such a way as to manipulate the hearers into following a certain path. Though He could, no doubt, have said exactly what was necessary to manipulate each individual hearer into doing His will, He never attempted any such thing.
We have arrived at the caboose - which indicates to you that the end is near, and is one of the most fun words in the English language (go ahead - say it out loud a few times! I can wait). Manipulation is a way of life for us. Whether in malice or in love, we nearly always choose our words and actions based on how we believe others will react to them. Sometimes it is blatant - I figure that if I offer to wash the dishes in front of the guests, my sister will choose to be gracious and offer to do them herself, allowing me to both look good and get away without having to do any work. Other times, it is a less selfish calculation that determines that the best way to invite someone to talk about Jesus is to pretend as though He isn't really that important to me, so that they won't be scared off by my crazy religious fervor (ha!). Whatever it is, though, it's never done out of true love - God Himself never gives us any indication that His communications with us are intended to fool us into doing what He wishes. What's more, any manipulative actions are performed with, at the very least, the (self-absorbed, and therefore not necessarily conscious) belief that we are (in at least some small way) mentally superior to and/or more crafty than the one we're manipulating, and usually also 2) an idolatrous attitude toward the desired goal and 3) a lack of trust that whatever we can bring about through a more honest and transparent approach to our neighbors is going to somehow be sufficient to accomplish God's (or our) purposes.
There's a lot more that could be said about who and how we manipulate (children -> parents, parents -> children, woo-er -> woo-ee, spouse <-> spouse, etc.), not to mention my proposed solution to my manipulative ways, but this train of thought is already too long to even leave the station, so I'd better get my fat butt off so that those of you who actually needed to get somewhere can be on your way!