  Small fluid leaks are common and frequently troublesome. We often consider
how to stop a leak, but here we ask a different question: how might a leak stop
itself? We experimentally study leaking flow transitions from continuous
drainage to spontaneous arrest. High-speed imaging reveals that fluid breakup
events generate droplets whose Laplace pressures oppose the leak. Early
droplets grow unstably, but a final droplet equilibrates to a stable spherical
cap via lightly damped harmonic oscillations. A total energetic theory shows
that inertia plays a key role in the leak-stop mechanism.
