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All embryos, from worms to humans, are shaped during development by morphogenetic steps that tug, bend, fold, and sculpt epithelial sheets into forms that resemble, or are the precursors of, the final adult structure ( 1 ). Most of these changes are the consequence of constrictions of the apical surfaces of epithelial cells that are powered by pulsatile contracting cytoskeletal (actomyosin) networks. On page 1232 of this issue, Roh-Johnson et al. ( 2 ) show that, just as in a car where the power of the engine is linked to forward movement by means of a clutch, clutch control is also the rate-limiting step for contracting cells in tissues.