Chem E.'s do it in packed beds. Chemists do it periodically on table Chemists like to experiment. Chess players do it in their minds. Chess players do it with royalty. Chess players check their mates.
Chiropractors do it by manipulation.
Choir boys do it unaccompanied. Clock Makers do it mechanically Clowns do it for laughs. Clu programmers do it in clusters. Cluster analysts do it in groups. Coaches whistle while they work.