public void setContactResponseSubtree(PhysicsLink rootLink,
            boolean desiredResponse) {
        verifyAddedToSpatial("change modes");

        PhysicsRigidBody rigidBody = rootLink.getRigidBody();
        rigidBody.setContactResponse(desiredResponse);

        PhysicsLink[] children = rootLink.listChildren();
        for (PhysicsLink child : children) {
            setContactResponseSubtree(child, desiredResponse);
        }
    }
Alter the contact-response setting of the specified link and all its
descendants. Note: recursive!
<p>
Allowed only when the control IS added to a spatial.

@param rootLink the root of the subtree to modify (not null)
@param desiredResponse true for the usual rigid-body response, false for
ghost-like response
jme3-jbullet/src/main/java/com/jme3/bullet/animation/DynamicAnimControl.java