For any instrumental ensemble (probably around ten people would be ideal) and one vocalist.
Procure a copy of the vocal score of any recent hit single, with the lyrics printed underneath the notes. With scissors, cut the score into its as many sections as there are individual bars, being sure to include the corresponding lyrics underneath each bar.
Distribute the score fragments amongst the instrumentalists, giving each musician an equal number .
A singer, actor, or vocal artist of some other sort should then intone the words of the song in order. Each musician should listen out for any words that appear on their fragments.
Upon hearing a word that appears on one of your score fragments, play the notes on that fragment in free time (even if your fragment refers to a different occurrence of the same word, eg, if words like "and" or "you" appear in several places in the lyrics, any bar which features the word "and" should be played every time the vocalist utters the word "and").
The performance ends when the vocalist has reached the end of the lyrics.