Answer:
Don't do this in the shallow end.
Long and think, red within, with a nail at the end.
Who is he that runs without a leg. And his house on his back?
Has feathers but can't fly. Rests on legs but can't walk.
I fly, yet I have no wings. I cry, yet I have no eyes. Darkness follows me. Lower light I never see.
It weighs next to nothing but no one can hold it for long. What is it?