Festo AirPenguin in action.
From Zero History:
The bugs, whatever those might have been, had never come, to his considerable relief, but now he saw, however briefly but with peculiar clarity, an aerial penguin cross the intersection ahead of him.
Something wholly penguin-shaped, apparently four or five feet long, from beak-tip to trailing feet, and made, it seemed, of mercury. A penguin wrapped in fluid mirror, reflecting a bit of neon from the street below. Swimming. Moving as a penguin moves underwater, but through the Latin Quarter air, at just above the height of second-story windows, Moving down the center of the street that crossed the one he walked on. So that it was revealed only as it crossed the intersection. Swimming. Propelling itself, in a gracefully determined but efficient fashion, with its quicksilver flippers. Then a bicycle crossed, on the street, going in the opposite direction.
"Did you see that?" Milgrim asked the cyclist, who of course was already gone, and in any case could never have heard him.