Vibrato!!!

Here is a very interesting collection of articles about vibrato.

I've found that one of the hardest things to do to a student is to slow down a fast vibrato.  What you basically have to do is ignore the learned vibrato and start again from the beginning.  Sometimes it may even seem easier to start a new vibrato from the right hand!  Of course that involves a host of problems, restringing your instrument, resetting the bass bar, learning to play left handed....