Systematic rotation of interface orientation angle. (A) Mean squared displacement of orientation angle change for interfaces with different starting orientations. (n = 918 interfaces, k = 3 embryos, see Fig. S3 A for boxplot of distribution of values at each angle range). (B) Mean rate of length change over interface orientation angle. (n = 5,355 interfaces, k = 7 embryos, see Fig. S3 B for boxplot of distribution of values in grey shaded areas). (C) Mean rate of rotation over interface orientation angle. (n = 5,355 interfaces, k = 7 embryos, see Fig. S3 C for boxplot of distribution of values in grey shaded areas). (D) Polar quiver plot indicating local direction of angle and length change, with streamlines overlaid. (n = 5,355 interfaces, k = 7 embryos). (E) Polar plot of a sample t1 transition with contracting interface in red and elongating interface in blue. (black arrow denotes starting time of t1 transition). (E′) Interface length over time for the same sample as above. (E″) Interface angle over time for the same sample as above. (F) Raw images of the same sample as above with false-color overlay of cells and interfaces. (Scale bars = 5 µm).