engagement invitation Riddles

My voice is tender, my waist is slender and I'm often invited to play. Yet wherever I go I must take my bow or else I have nothing to say. What am I?

Every day, a woman was seen crossing the border carrying bags of sand on a bicycle. After some time, the border police become suspicious and stop her, but found she only had sand on her, so they let her go. Years later, they get a mysterious invitation for a party at a large villa. The owner comes out to greet them, it is the woman that has been crossing for years! How did this happen?

A man owned a casino and invited some friends. It was a dark stormy night, and they all placed their money on the table right before the lights went out. When the lights came back on, the money was gone. The owner put a rooster in an old rusty tea kettle. He told everyone to get in line and touch the kettle after he turned the lights off, and the rooster will crow when the robber touched it. After everyone touched it, the rooster didn't crow, so the man told everyone to hold out their hands. After examining all the hands, he pointed out who the robber was. How did he know who stole the money?