DOCTOR: Cellular dissemination.

SARA: Cellular what?

DOCTOR: To put it in lay language, cellular dissemination means our bodies were broken up by some process or other, shot through into the fourth dimension, and at a given point, reassembled again on this planet.

STEVEN: That's fantastic.

SARA: Impossible.

DOCTOR: Fantastic it may be my boy, but impossible, no, because precisely that is what has happened.