Quote Originally Posted by Riverkilt
On the bottom of the blade there's about two inches of sawtooth like grooves near the handle.
The "technical" term for the filework is "jimping," and it's where you put your thumb to get more leverage and finer point control when using the knife. On a full-sized dirk, it's more decorative than on a sgian dubh - the jimping is actually useful on a sgian dubh, but on a dirk they usually cut the jimping too deep, too far apart, and far too high up the blade to be useful.

Some people will tell you it's for scaling fish. They'd be wrong.