Dean's double-take probably couldn't be more obvious, a stunned wait, what? headspin and harsh swallow (which almost turns into a cough as it meets an incredulous splutter coming the other way), and... seriously, are normal people civvies retarded or something? He doesn't get how this isn't screaming 'weird' to them, how people aren't making more of a fuss – every household on the block losing a kid is strange enough, but in the same day? That's a full-blown evil omen.
He does, at least, manage to bite back the urge to ask what the hell the parents were doing while their kids were being goat-knapped. Ironic that might be, sure - holding everyone else to these crazily high standards - because John wasn't ever exactly Father of the Year... but he made a point of not leaving Sam defenceless, and the 'look after Sammy' mantra's almost indistinguishable from Dean's heartbeat now.
Of course controlling that - trying not to destroy whatever tentative bridge knowing Lea's built for him – means something else, slightly less stupid, slips out. “And no one else saw this goat-thing?”
Clearly Dean has a lot to learn about interview technique.