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To determine the egg capsules' various properties, Rapoport put them through a series of stress tests. He measured the mechanical hysteresis of the capsules, the energy that is dissipated as the capsule material returns to its original shape. Think of a rubber band being pulled. There is energy being transferred to the material as it is being stretched. When the rubber band is released, energy is released, though some of it is expressed as frictional heat. That energy track can be plotted as a substance is pulled and then allowed to retract. The capsules, probably as a response to the waves that batter them, have an unusual dual-nature mechanical response. This phase consists of high stiffness that becomes one of rapid energy dissipation as the the material gives way under greater stress. These properties are consistent with other shock-absorbing materials.

In the tests, Rapoport used a device called a tensometer, which clamped its "fingers" around slivers of capsule material. The machine pulled on the pieces in short bursts and relaxed in rapid fashion, dozens of times in a minute, "jiggling them at different frequencies," as Rapoport put it. In repeated studies, the capsules endured long-term cycles of stress. They showed a rare ability to return to their initial state after being stretched beyond the point of apparent failure, the point at which some materials become permanently deformed, like a metal spring pulled irrevocably out of shape.