How much force does it take to stab somebody to death?

Here is a review of an absolutely crazy arXiv preprint:

"A number of groups have attempted to measure the forces necessary to penetrate skin but the results are difficult to apply to murder cases because of the sheer range of factors at work. The type and sharpness of the knife; the angle and speed at which it strikes; the strength of skin which varies with the age of the victim and the area of body involved; these are just a few of parameters that need to be taken into account.
...
They [the authors, by Misha] have developed a machine that measures the force required to penetrate skin–either the animal kind or an artificial human skin made of polyurethane, foam and soap. The surprise they’ve found is that the same knives from the same manufacturer can differ wildly in sharpness. And the force required for these knives to penetrate the skin can differ by more than 100 per cent."

This is definitely the strangest preprint I've ever seen...