River's rigged up a film loop from the cameras inside the vault, four seconds, which the Doctor identifies as an Angel, "hands covering its face," which he only says as a clunky way of telling us to watch its hands and its face. He recalls the time with Sally, but notes that in that case they were "scavengers, barely surviving." (Also, they were cool and interesting and didn't move when we the viewer were looking at them, and they killed you by sending you back through time instead of just being super mean. The regular ones we're meeting today have very little in common with them.)
We run through the whole thing about the Angels, River being sweet with Amy as she asks Excellent Questions about how they're not really "just" statues unless you're looking at them, and we learn that this particular one on the video loop is a dormant collector's item, pulled from the ruins of Razbahan at the end of the last century. "There's a difference between dormant and patient," the Doctor says scarily, and then explains the central plot hole in this story: "It's a quantum lock. In the sight of any living creature, the Angels literally cease to exist. They're just stone."
Which is not exactly true, because when they move, which this is very stupid, they are still just moving statues. So anything you think is scary about them, no longer scary. And the only reason they're here at all, in a story that manages to strip out all the least interesting bits of the Vashta Nerada and present them as something new, is because somebody bought Moffat a drink or something and gave him props on the Weeping Angels, and instead of thinking about what was actually cool about that story, decided that the Weeping Angels -- and no doubt the merchandising opportunities they present -- were themselves what made "Blink" cool. Which, it's one thing to misunderstand what works in somebody else's story, and twist it, but how fucked up is it that you could take your own awesome story and stripmine it like you'd never even seen it before?
But then the Doctor says this is "the ultimate defense mechanism," and it's Amy that says, "What, being a stone?" Which I can't help but think works on two levels, since that's what she did. (Echoes of Jackie's "we get hard," in the Elton episode, which was it turned out less about getting blowjobs from concrete and more about what happens when you lose Bliss in pursuit of the Doctor. Elton is an Amelia that never became an Amy; he was saved from that fate or became something worse, depending on your point of view.) "Until you turn your back," he nods.