Ari had a brilliant idea for a way to run chorus rehearsals. Soloist selection will be at random for each piece, but you won’t know if you have a solo until it’s time to sing it.
The corresponding conducting technique is to give the upbeat and then on the downbeat suddenly point at the soloist-to-be. This technique is adapted from a certain conductors-who-will-remain-unnamed’s habit of switching soloists at the last minute. The advantage is that everyone will be looking up out of their music, so it’s not all a wash.