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Editor's pick Ideas on the meaning of cave art hand stencils 18 March, p 38 From Greg Watson, Albany, New York, US You report that prehistoric hand stencils on cave walls with various digits missing could represent a sign language. From Linda Dawe, Chesham, Buckinghamshire, UK The cave stencils look like tic-tac hand signals used by bookmakers to communicate betting odds at race courses to me. My granddaughter learned sign language before she could talk, and the recent television series Chris Packham's Animal Einsteins showed hand gestures that were identical among chimps, bonobos and human toddlers. [Extracted from the article]