CW, it is most interesting that you used the word "gibbet!" Certainly Wikipedia http://en.wikipedia.org/wiki/Torture_stake has some interesting things to say about it!
I have even considered that the criminal was basically suspended over a pointed stake centered upon the area of the anus? Then as the arms and legs weaken the victim is literally forced to impale his person upon the stake!
But, perhaps I just a little too barbaric?
But, it may also be no more than the remarks of some one or some group who decided to make exposure to the "stocks" even more deadly?
© Charles N. Pope, US Library of Congress. All rights reserved.