Closed bilayer membranes (vesicles) display a plethora of non-spherical shapes under equilibrium conditions, unlike drops and bubbles which are kept spherical by surface tension. Even more complex behaviour arises under applied flow. Intriguingly, a vesicle can adopt asymmetric shapes even under symmetric forcing such as uniaxial extensional flow. Narasimhan, Spann & Shaqfeh (J. Fluid Mech., vol. 750, 2014, pp. 144-190) explain the mechanism of this peculiar instability and trace its origin to

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... he tension which develops in the area-incompressible membrane in response to the applied stress. The authors also show that this mechanism is relevant to the pearling of tubular vesicles. This study raises many questions, e.g. whether other soft particles with load-dependent tension such as capsules can undergo similar shape transformations.