Tom watches the Doctor and Rose investigating from inside -- from behind a Union Flag in his window -- and what they are doing is sniffing. Well, the Doctor anyway, while Rose giggles: "Want a hanky?" He asks if she can't smell something, and she finally notices it: "Sort of metal?" He nods, and they take off with a cheeky wave to Tom's dad. Remember? Like in "The Idiot's Lantern"?
In a narrow alley, where Danny Edwards disappeared -- "Cycled in one end, but never came out the other" -- the Doctor feels the feeling again: "Look at the hairs on the back of my manly hairy hand!" Rose smells the smell again: "Like a...a burnt fuse plug or somefing." The Doctor nods: "There's a residual energy in the spots where the kids vanished. Whatever it was, it used an awful lot of power to do this."