Heh, my mentor, when I was learning how to sharpen knives, shouted that at me when I was going to test the edge of the blade with my thumb. His idea of "taking his student over his knee" was making us do the most tedious part of cleaning up old blades. Having to take the scrub brush and cleaning oil to scrub off any and all rust we found. It took ages, and the oil smelled bad. It was a necessity, but the cleaning oil was harmless and it was just that it was grimey and tedious.

Heh, hated that job, but I promised not to do that again. And yeah, don't test the edge with a thumb, that's a quick way to get hurt.