We have an anecdote about that, from Wneighbor's son-in-law, I believe. I think it was the solid "click" of the CRKT knife that did it.
I think the twisted thinking of the enemy goes something like: "These are Americans. They're not allowed to shoot me. But nobody told me anything about knives. I don't want to risk a couple pieces of my anatomy to find out what they might do with even a small knife".
Heh.