David,
Your right there are many things you could fill up a keris with, oil, sent,spirits, wishes etc
If any of you have watched the dvd "the ring of fire" you will probably recognise the guy in the video link I have provided. At one point in this new footage he communicates with the keris isi and as a result the keris moves all by itself.
I know it could be faked but I think I believe in him
http://uk.youtube.com/watch?v=Aos0hnwiHt8