I was just looking through "So You're Going to Wear the Kilt", the section about dirks and sgian dhus. He ends the section with:

"The blades of most skean dhus have, like the dirk, longitudinal blood grooves and nicked backs which are supposed to be fish scalers. This is a bit silly. The dirk is a stabbing weapon, so blood grooves are functional, but they are quite out of place on a utility knife. And anyone who knows how to scale a fish knows that the implement to use is a teaspoon."

This is a bit silly indeed. The filework on the back is called "jimping", and is to provide the thumb with a bit of traction while manipulating the blade. As for "bloodgrooves", the proper term is "fuller," and they are to stiffen and lighten the blade. They have nothing to do with blood.

I'm sure several people here know this, but thereare probably also some who don't, or never thought about it.