I have always enjoyed reading about the non-material aspect of kerises, though somehow, I just can't remember much of them to retell them to others.
On the vibration of the kris from time-to-time, I can't help but recall a particular meeting room in the building that I work in. The window panes would rattle whenever a truck drives by. Many a visitor would ask - "Was that an earthquake?".
I guess the meeting room was situated at the exact spot where vibrations converge.