This exercise is a nice variation on “The Infinity Loop”.
Here’s how it works:
Begin with three or four players. The first player establishes a groove and plays a repeated pattern. Then, one at a time, each player enters the improvisation, either imitating or adding something new. Once each member of the group has entered, allow a few minutes to groove in that space. Then, the first player makes a change. They might want to add a few new notes and take the original melody into new harmonic territory, or they may want to change the tempo by speeding up or slowing down. Once they make this change, each player now changes with them, one at a time. So, player two now imitates or adds something new to this new groove, and around we go. Each time the entire ensemble has adjusted, player one changes again. In this way, each player is listening for the changes to come, engaged in the music and on edge of their seats ready for the new elements to be added. This form is a nice way to introduce the idea of melodic soloing, because each new element can also be seen as a solo played by each individual player.