[ryandv]

    Indenting with a metallic indentor gives a quite distinct
    response in both of these phases. In the elastic phase, the sponge
    regains its original shape following unindentation over a timescale
    t given by the relaxation timescale of the visco-elastic polymeric
    material. For the polymeric materials used, the relaxation time-
    scales are of the order of 100 s and the material recovers fully
    leaving no trace of damage. In contrast, the pseudo-plastic phase
    retains a permanent deformation as the relaxation timescale
    effectively goes to infinite due to frictional locking. This deforma-
    tion memory can be erased by removing the external strain field
    allowing the pseudo-plastic zone to transit back into the elastic
    zone through the removal of applied global stress on the sponge.

To take the analogy further, you have to squeeze the metal pins together first so that they rub together and the friction prevents them from all just falling back into their original position after a minute or two once you remove your face from the pins. Instead of shaking it up you stop squeezing the rods together and eventually they all fall back into their original position. Someone with an actual materials science background can take it to the next step.