>>384744991
As the other anon pointed out, use the _Stretch parameter on the physbone to drive the animation. If just want to do a binary blendshape on/off then just use the parameter as a transition condition in your animator. If you want it to be a scaling thing, like the blendshape value corresponds to how far the stretch is, then you can set that up with a blend tree in the animator. Refer to a radial puppet tutorial such as https://www.youtube.com/watch?v=EkVlkrQ6ypE ; do the same thing but simply use your _Stretch parameter instead of adding a new menu entry.