Answer:
Long and thin, red within, with a nail at the end.
Usually green but can be brown. It's a great place to play or lie down. What is it?
The more you have of me, the less you see. Who am I?
They are the shore's gallant knights.
Tickle with your fingers and a song it will sing. Be careful, though, you may break a string. What is it?
My days are numbered. What am I?