While walking on the beach in Monterey, I have noticed several Sandpipers that I at first thought had lost a leg; they hop along on the one, eliciting pity from naive onlookers.
Then, though, they stretch their other leg back down and begin walking as normal.
Why do they do this? Are they resting the leg they retracted? Are they playing a joke on us gullible humans? Are they feigning being one-legged for some other reason?