Simple motion inside biological cells, such as the streaming of cytoplasm—the liquid cell interior—is widely believed to be essential for cells and the development of complex organisms. But due to the lack of suitable tools, this intracellular motion could so far not be tested as hypothesized. Now, a team of researchers from the Max Planck Institute of Molecular Cell Biology and Genetics (MPI-CBG) in Dresden found a way to induce and control motion within living cells and early embryos. Rather than using microscopes simply for observations, the team around Moritz Kreysing managed to actively guide central developmental processes in worm embryos by a new cell-biological technique called FLUCS. This new microscopy paradigm paves the way towards a systematic understanding of how complex organisms develop and what keeps them protected from malfunction and disease. These findings were published in the current issue of the journal Nature Cell Biology.