I have to admit that I wasn't aware of the amazing abilities of sea cucumbers until this story came up. Their skin is normally flexible, but in response to a stimulus it can get very stiff within a second.* Recent findings suggest it's the interaction between collagen fibres that is switched on and off.
Researchers in the US have now succeeded in mimicking this behaviour in a new material. Read my news story here (free access).
* Chinese traditional medicine has drawn the obvious conclusion from this and uses dried sea cucumber as an aphrodisiac! (according to the Wikipedia entry)