Just a quick one. If you think you can quickly and quietly poison someone with arsenic, head over to The Chirurgeon's Apprentice for a good description of how people actually die from it. It's extremely unpleasant and nothing like the undetectable weapon of choice we often think it is. Even small doses ofter a long period of time will cause symptoms, although not as violently as an acute poisoning.
And all thoughts about murder aside, The Chirurgeon's Apprentice is a great blog for anyone interested in history and medicine. It also makes you really, really happy to live today and not, say, 150 years ago.