Back Bay Patch reports a man showing a woman how to open a folding knife at the Crossroads on Beacon Street early one recent morning wound up stabbing another patron in the leg.
I'm not sure how someone could stab someone else in the leg while teaching someone how to open a folding knife, although cutting yourself in the hand accidentally while trying to close it is a possibility. I'm also not sure how a folding-type knife could cause that serious of a leg wound unless you had the extremely bad luck to nick the femoral artery or something.
People tend to use balisongs (a/k/a "gravity" or "butterfly" knives) as "fidget toys" and to do "bar tricks" and such with them, which could lead to accidentally dropping it and stabbing someone if you're doing it in close proximity to another person.
The report said after showing her how to open a knife he demoed how to stab someone with it. It sounds like he was stabbing the air when someone got in the way.
This reminds me of the classic simsons line:
Lisa: OK, then I'm going to start kicking air like this. [kicks] And
if any part of you should fill that air, [kicks] it's _your_ own
Homer: All right, pie. I'm going to start doing this ...
and if you get eaten, it's your own fault.
The suspect is (was) the executive chef at Clio. He was let go for his part in this.