You Tube seems awful these days. Most videos do not play without a long delay. There is a 30 sec audio clip in link but it is almost not worth the bother.
Playing with the back of my left and right tongues I am trying to get one side to vibrate then the other. I switch back and forth and on occasion I am not doing what I think I am doing. I can manipulate the tongue to rub the left edge along my upper and lower left teeth without problem like everyone else. Also I can use the tip of the tongue on the outside of left gum of the left teeth yet I was unable to vibrate the left tongue until recently. The right tongue is easy to vibrate and it has always been that way. Almost like I have a functional hole in my use of my left tongue.