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WikiPedia: Echo (voi) http://www.elephanttrust.org/sites/elephanttrust.o... http://www.bbc.co.uk/nature/characters/37 http://www.thesun.co.uk/sol/homepage/features/3082... https://archive.org/details/mindinganimalsaw00beko https://web.archive.org/web/20110202130628/http://... https://www.pbs.org/wnet/nature/episodes/echo-an-e...