 Amorphous materials exhibit complex material properties, including plasticity, which is controlled by the density of weak spots in the material. The density of weak spots can be determined from the geometry of an amorphous structure alone, and this approach has been applied to quantify cell packing geometry in the developing wing epithelium of a fruit fly, suggesting that this tissue exhibits plasticity and non-linear material properties that emerge from collective cell behaviors. This article was authored by Marco Popovich, Valentin Trujell, Natalie Adai, and others.