Rephrasing means saying the same idea in a different way. Here are three simple ways to say "Some rays flap their fins up and down like birds":
- Some rays move their fins up and down like birds flapping wings.
- A few rays wave their fins up and down just like birds do.
- Some rays beat their fins up and down the way birds flap.
They all mean the same thing — the rays move their fins like birds move their wings.