C•A•B-droplet sample solution (2.4 µL) was placed in the 5 mm hole of the observation chamber. The sample solutions were covered with mineral oil to prevent evaporation. The chamber was incubated on a stage heater at 60°C for 30 min and 63°C for 15 min to increase the fluidity of the DNA droplets. After incubation, we added 3.6 µL of a division trigger mixture to the sample solution in the chamber and observed it at 63°C. Depending on the experiment, different division trigger contents and concentrations were used in the division trigger mixtures. The experimental details are described in Supplemental Methods S3.