I'm guessing none of you have used a shaper?
At my first job, I was running a 2.5" cherry chair seat through a shaper with a 2" radius cutterhead. Well, either a guidepin broke, or I lifted the piece just a touch, and that 15 pound piece of wood shot off across the shop like a rocket, leaving me shaking!
I'm still shy with the shaper. Everyone I've worked with in furniture shops agree that the shaper is the scariest tool. A master who taught me a lot of what I know (Phil Lowe - you've probably seen him in Fine Woodworking) used to wear a plywood apron when using the shaper, because the knives used to just be held in by friction. They didn't have the threaded teeth on top like they do now. So occasionally this steel blade would come flying out of the machine right at nut-level, like a japanese throwing star!