I'm a staunch supporter of health and safety in the shop and always
appreciate reading posts about mistakes, in hopes that others will benefit
and not repeat the screw-up. I've been lucky, but here goes:

I bought a plate jointer. I went to try it out. So I got a few pieces of
pine board out of my scrap bin, and proceeded to cut some slots. I'd read
the recent article in FWW and knew what I wanted to test.

I cut several slots in the edge of a few scraps; everything went perfectly.
Then I tried to cut a face slot in a small piece of scrap (the scrap 5" X 6"
piece laying flat on the bench). I set the board on my bench and used a
support fence (like in the article), and plunged.....

.... into a unexposed knot. The board and plate jointer blade bound, and the
board flew into my chest (OK..... my belly) with considerable force.
Pluswhich, the inertia carried the blade into my workbench, which now has an
ugly asymmetrical gouge that kinda' resembles a biscuit jointer slot with
an extended right side.

Live (hopefully) and learn (hopefully). Be safe all.

-JBB