While Amy and the Doctor break into the Big Mining Thing, Ambrose explains a sort of gross country-folk story about how her dead uncle Alun was meant to be buried with her dead aunt Gladys but when they dug her ass up, it was gone. "Body, coffin, everything." But there was no sign of disturbance on the surface, we're told by the I guess keen-eyed tracker Ambrose. Rory, being an idiot, asks her to explain that entire thing again. Ambrose, having been married to Mo for at least ten years, does so without blinking.
The ground still doesn't feel like it should, but Amy advances the theory that ten years in the future, that's what the ground feels like. I like this theory. The Doctor eats some blue grass and then spits it out again, making her giggle, and they are cute for a second. Further in, to where the random holes have begun appearing, we meet Nasreen and Mack. Everybody asks everybody who the hell they are for awhile, psychic paper, the Doctor realizes that blue grass + random holes + BMT = danger, but speaks as elliptically as possible about the reasons and qualities of this danger for a good while as everybody runs around panicking.
Seems the ground is attacking. The Doctor tells Amy not to fall in the holes. So she does.
Ten minutes of Artax and Atreyu later, the Doctor cries into his pudding for awhile and then straightens up and continues refusing to explain one single solitary thing that has happened so far, while everybody how fucking stupid they are. It's still rude and not funny, and it still does nothing to further the story.
And his opposite number, cruddy little Elliot, starts pacing around the grave where Rory is, talking all this "When you've eliminated the impossible whatever remains," bullshit of the sort unlikely precocious kids on bad TV shows are always affecting (at least Elliot references how he likes the audiobooks of Sherlock Holmes, so it's not a total waste), and basically the graves are eating people.
So the deal is that when the drill hit the 21k mark or thereabouts, it activated certain "bioprogramming" in the dirt of the valley, which made it start eating people. Egregious: "Bioprogramming! Clever. You use biosignals to resonate the internal molecular structure of natural objects!" (Oh right, biosignals.) Anyway, Nasreen being a Woman of Science she is not having it, but the Doctor is still having Atreyu aftershocks, so he's flummoxed. But then even though the drill is stopped, there's still drilling happening, and the Doctor cutely lays down on the ground to confirm it: There's now somebody down there drilling up. Having been warned, no doubt, by the resonation of the "internal molecular structure" of "natural objects."