A tiny shared composition can begin with a decision rather than a melody. Try making a short sequence in which two people take turns choosing what happens next without discussing the whole plan.
Give the game a clear boundary
Use three quiet, familiar sounds you can make comfortably. Agree a signal for finishing and a maximum of six turns each. One person plays a sound; the other responds with any of the three. Leave enough space to recognise whose turn it is.
Keep this first version free of scoring or competition. The purpose is to notice choices: repetition, contrast, hesitation and the temptation to predict your partner.
Talk after the final sound
Each person can name one moment when the sequence went somewhere unexpected. Did you repeat a sound to support the other person, or because you had not decided what else to do?
Play once more with the starting person reversed. Save a short written description if you want to remember the experiment. The result need not become a polished track. It offers a small experience of making musical decisions together while discovering how much a response can communicate without an explanation.