Halfway! ...
What’s the difference between a duck?
By googling the riddle, I see some nearly correct answers, taking mine as correct, of course:
“One of its legs are both the same.”
I defend this as the correct answer because of the pivot around “legs” . We have “One of its legs ...” and “... legs are both the same” as grammatically intact phrases.
This much of the riddle is rational!
I was going to say “the height” but google reveals the true answer. Good one.
Why a duck?
https://www.youtube.com/watch?v=v3hjo7V7TPs
One of his feet are both the same.