Like the replicants on Blade Runner, it's hard to spot a fake Emperor Penguin. The task requires careful study by a specialist. But if you watch carefully, you'll notice that the second from the left in the group doesn't move like a normal penguin.
For the BBC nature program Penguin--Spy in the Huddle, zoologists and, presumably, invasion planners, planted 50 cameras among a colony of Emperor Penguins in Antarctica. Many of these cameras were disguised as penguins themselves, thus gathering information and sowing distrust within the justifiably paranoid penguin community.
-via Twisted Sifter