<p>A tiny worm that can regrow its body if chopped into little pieces could help explain how human stem cells function and could lead to better ways to manipulate them. Research has found that a molecule gives the stem cells of the worm, known as a planarian, regenerative power. A planarian can grow an entire new worm from a tiny piece of any part of its body except for the pharynx (a digestive organ) and the region in front of its light-sensing eye spots.</p>