Your Shadow

"Your shadow, it is always there beside you. even when a dragon flies really high up their shadow is still below them."

"That is correct" Stardust answered. "Your turn, give me a hard one"

You think of a bit then you think of a riddle that would be really easy for you but almost impossible for a dragon. "Which creature has one voice and yet becomes four-footed and two-footed and three-footed?" you ask.