A sign on the door might have helped. Something like 'Free Knife 
Sharpening Lessons' maybe

Don

Our comforting conviction that the world makes sense rests on a secure
foundation: our almost unlimited ability to ignore our ignorance.
Daniel Kahneman, Thinking Fast and Slow

On 2015-07-06 7:12 PM, Gye Greene wrote:
> Well -- I admit, there*were*  two sessions where I was sharpening a
> colleague's kitchen knives.  So maybe it was one of the "knife days" that
> freaked someone out.