At the conclusion of The Pandorica Opens, the penultimate episode of Series 5 of NuWho, just as River Song pulls open the doors of the TARDIS to reveal a rock face blocking her escape and mere seconds before the TARDIS explodes, a hoarse, evil sounding voice intones, "Silence will fall!" As one, the viewing audience thought, "Ooh, a mystery that will surely be explained in the next episode or, at the very least, the next series." The audience was wrong. Never one to produce scripts that merely pander to audience expectations, Moffat instead elected to take the story in an entirely different direction, only explaining later that the origin and owner of the voice were not important. It was sufficient, apparently, to know that the Silence were somehow the culprits, even though they don't sound like that voice and even though viewers were never shown how they managed to destroy the TARDIS. The old adage of showing, not telling, was never so far from consideration in the mind of the Moff. Strangely, though, the voice in the TARDIS sounds a little like Prisoner Zero from Matt Smith's opening episode, The Eleventh Hour. But that's probably just coincidence. Curiously enough, the back story of Prisoner Zero, as well as how it knew about "silence will fall" in the first place, was also never explained. Let's raise our collective hands in exasperation, cry out, "Oh well, I guess Prisoner Zero was just really well informed and blowing up the TARDIS is so easy that anyone can do it..." before fetching our metaphorical brushes and lifting up the edge of that carpet. Because the show will never mention that plot point again, let alone actually show viewers what really happened, since showing viewers what happens isn't generally the norm in a visual medium like television.