Sheets of epithelial cells allow animal tissues to define inside and outside, and as such are arguably the fundamental building block of metazoan life. Because of this topological role, the folding, stretching, and on occasion disruption of epithelial sheets is a central feature of both embryonic development and tissue regeneration. In this study, Carter et al. (1) examine a particularly intriguing example of epithelial gymnastics, mouth opening in the freshwater polyp, Hydra vulgaris.