where they graft the Doctor with another holo matrix to try to stop his program from destabilizing. they think it failed, losing his memetic identity entirely until the end, when they hear him whistling which was not part of the original program.(funnily, think the episode name was Lacuna
)And they used this trope again in a Star trek Movie, killing data but having his lesser duplicate start humming the very same tune data failed to summon in his very first appearance... and iirc AGAIN in ds9 though the situation alludes me currently,