This is always a topic I find interesting and have my own ideas on the subject. The mind is a very powerful thing in either the controlled or uncontrolled state.
For those who have not seen this video, it is worth the watch and without the first hand experience of being there, I am sure it can for the most be taken with a grain of salt...
Keris are mentioned and shown briefly just past the 5 minute mark...nothing ground breaking but it is interesting.
https://www.youtube.com/watch?v=Oam9wCFFids
Gavin