Helpful Hints from joeeze: How to tell if a knife is sharp or dull — without drawing blood

I read this in some food-centric magazine a long time ago but it seemed practical and easy to do and so I bring it to you for your scrutiny.

Hold the knife loosely by its handle between your thumb and forefinger, then draw it across a tomato such that the only force exerted on the tomato is that of the weight of the blade.

A sharp blade will cut the skin; a dull blade will indent but not break it it.