If you want to have that turn on and off, you animate the Influence of the resulting Soft Body modifier.
While that will be possible in 2.5 (hopefully, I tried to see if it is with my set up in 2.5 build, but couldn’t figure out a way to do it), you have to use a bit of a complicated set up to do this … And also Enrico’s use of softbodies is great for fat jiggling characters, not so good for tails and antennae …
In the example below I have set up a “softbody driver” which is a simple line subdivided once so it has 3 verts to weight for the softbody modifier . They all belong to a vertex group named “Group” which is the goal for the softbody . The weights for the right 2 verts are below 1.0 (just play around with the values until you get the desired effect) .
To that line I have vertex parented an empty to each vertice . These act as the drivers for both the beveled curve and the armature .
In the curve the end empty acts as the hook on the last control point . You could also hook the middle control point and also animate the hooks independently to get control of the mesh, but that will not give you very precise control in the end (which is why I didn’t do it) . Using armatures is a bit more predictable .
With the armature the empties act as the constraint targets to the bones that are the IK targets to the B-bones . You can get control back of the armature by keying the influence of the copy location constraint that makes the IK targets follow the empties .
Alt-A to bake the softbody simulation to frame 250 . From 250 to 275 the influence of the constraint is keyed out to 0.0 .
floppy.blend (173 KB)