Can you get a musical (ish) sound from it? Pull the cup so that the string pulls very tightly against the table leg.
How does the sound compare to what you heard with just the string and no cup? Work in pairs each with a cup instrument. Put the loose end of your string through the hole from the bottom, tie the end of the string that is inside the cup to the paper clip and then pull all the extra string out of the cup so the paper clip is on the bottom of the cup. Take each cup and poke a hole in the bottom.
