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Ask most people to identify the fastest animal on Earth and they'll suggest a cheetah, falcon or even a sailfish. To that list of speedy animals researchers would like to add the Spirostomum ambiguum, a tiny single-celled protozoan that achieves blazing-fast acceleration while contracting its worm-like body. Common to many lakes and ponds, the Spirostomum ordinarily moves about using tiny hairs called cilia. But its claim to speed involves extremely rapid acceleration while contracting its body when startled. The creature can shorten its body by more than 60 percent in a few milliseconds, going from a four-millimeter flat ribbon to the shape of an American football -- all without the kind of muscles humans use. How it does that, and how it does that without damaging fragile internal structures, are questions researchers are seeking to answer. The physics and mathematics of the answers could help advance nanotechnology and accelerate a new generation of robots barely large enough to see with the naked eye.