How can I make a telephone with cups?

To make a telephone with cups, you will need two cups, a long piece of string, and a sharp object like a nail. Poke a small hole in the bottom of each cup. Thread the string through the holes and tie knots on the inside to secure it. Pull the string tight and talk into one cup while the other person listens through the other cup. The vibrations from your voice will travel along the string, creating a simple homemade telephone.