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Broton effects a change into the likeness of the Duke of Forgill using the latter's body print. (TV: Terror of the Zygons)

A body-print was the image of a form used by the Zygons to assume the likeness of others. The technology associated with this assisted the natural shapeshifting abilities of the Zygon.

It was essentially a biotechnology which acted as a bridge between a given Zygon and a life-form they wished to emulate, and imprinted the original onto the copy. The "originals" would be kept in stasis, attached to a machine. A Zygon could then access the machine remotely and request the shape of any life-forms then hooked up to it.

The individual whose body-print was being used had to kept alive as the likeness wore off every two hours, necessitating its re-assumption. (TV: Terror of the Zygons, PROSE: Sting of the Zygons, COMIC: Rest and Re-Creation) When killed, a Zygon would lose its link to the body-print machine and thus revert to Zygon form. (COMIC: Skywatch-7)

More acessible portable-hand-sized machine parts were later created. (HOMEVID: Zygon: When Being You Just Isn't Enough)

If the body-print machine itself were damaged or destroyed, Zygons could still shapeshift, but only in a limited fashion. Using solely their natural abilities, they could maintain a given form for up to two decades, but they lost the ability to transform into anything else, or to revert back to Zygon form. (AUDIO: The Zygon Who Fell to Earth, HOMEVID: Zygon: When Being You Just Isn't Enough)

The Daleks used body-prints too to create duplicates. The originals were not required to survive to maintain the duplicates. (AUDIO: Out of Time)