The speed with which they were mimicked suggests these expressions were involuntary, Biology Letters reports.

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This new study, published today in the journal Biology Letters shows how they do it.

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Joyce and his colleagues detailed their findings online Wednesday in the journal Biology Letters.

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That is a question addressed by Isabelle Dean and Michael Siva-Jothy of Sheffield University, in Britain, in a paper in Biology Letters.

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The results show that the mole's second thumb is not a real digit but starts out as a wrist bone, the scientists report in Biology Letters.

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Their results are about to be published in Biology Letters.

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The research is reported in the journal Biology Letters.

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The study, published in Biology Letters, backs previous theories which suggest male sheep's horns are curved to withstand head-on clashes, while female sheep's horns are spiked in order to push competitors away.

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Another study just published in Biology Letters, by Sarah Kilgallon and Leigh Simmons at the University of Western Australia, has, however, thrown light on a previously unexplored part of the male side of reproduction.

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In one study published recently in Biology Letters, chimps and bonobos presented with a food-based ultimatum game would accept any food reward on offer - no matter how meagre their share was in comparison to their partner's.

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