Explain · analogy · Serious version
Do penguins have knees in terms of a person in a very long coat
Penguins do indeed have knees tucked away inside their bodies, structured exactly like the legs of a person wearing a very long, oversized trench coat.
The skeletal anatomy of a penguin is effectively a bird crouched in a permanent state of standing, with the femur, knee, tibia and fibula hidden beneath a thick layer of feathers and blubber. It is functionally identical to a man wearing a coat that reaches his ankles, where the knees are permanently bent in a half-squat inside the fabric. Because the bird is built for hydrodynamic efficiency, the legs are tucked tight to the torso to maintain a streamlined profile, rather like a spy concealing a folding bicycle beneath a heavy wool garment.
This arrangement forces the penguin into its characteristic waddle, as the knee joint cannot fully extend while the bird is on land. Just as a gentleman in a floor length mac finds it impossible to stride with the vigour of an athlete without tripping over his own hem, the penguin is restricted by its internalised geometry. The joints are perfectly functional, they are simply perpetually flexed to keep the centre of gravity low and the profile aerodynamic for diving.
When the penguin finally reaches the water, it abandons the stiff, restricted gait of the fashion-conscious spy for graceful swimming. It uses its legs as rudders to steer, finally getting some use out of those knees that have been spent staring at the inside of a parka all morning. It is a biological quirk that turns every Emperor penguin into a tuxedoed pedestrian who is perpetually sitting on a phantom chair.
Where the analogy breaks downA penguin uses its knees for powerful propulsion in water, whereas a person in a trench coat mostly uses them to find the nearest exit.