First I will say I'm not in favor of capital punishment. As much as I want to strangle some of these sick and twisted criminals on death row, I'm not convinced that our justice system is foolproof enough to guarantee we would only execute the guilty.
Maybe I watch too many crime shows.
I also remember discussions that the guillotine was not as humane as one might think. Given the forms of execution practiced to that point in history, it was far better, but it wasn't perfect. Some argued that the head was severed so quickly that the body didn't die right away. I mean, we don't even have a complete agreement on what it means to be declared dead. Is it when the brain stops functioning? Probably, but how long might the brain function after it is severed from the body? http://www.historywiz.com/guillotine.htm
I'm sure there is a better, more accurate, accounting of the guillotine than this site, but it was short and aligned with what I had learned previously, so I thought I'd share. Maybe someone with more history background would care to ellaborate.