Then you read it wrong. It was never left open for your personal interpretation. As I said in my last message, the founders left behind writings that made these things clear. In addition, you'll find that men who the founders openly admitted were influencial, left behind a wealth of information. Obviously, you're not familiar with any of them. I'll leave you to you own research.
However, I'll give you some tidbits that you can affirm. All methods of execution that weren't designed to bring about the direct and immediate death of the condemned were banned. In various writings, from various framers and their influences you'll find direct references to drawing and quatering, disembowelment, being burned at the stake, being bled to death, drowning and others. You're particular fetish for the slow death of a man trapped by his penis in a log isn't mentioned, but I think it's reasonable to assume that such sickness wasn't even considered by those who established this great nation.
If you're truly clueless as to where to start. I would suggest the Annals of Congress, 1789 for a start. Then perhaps the house and senate journals for the same year. Both are available either electronically or on microfilm at most larger libraries or any university library. You'll be surprised at just how specific these men were in their intentions and just how wrong you are.
Well, I happen to believe that it is you who are wrong here. Thus I stick to my reading.