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A team of scientists in Hungary, who have been studying dog behavior for the
past decade ,believe that dogs are more intelligent than people have previously
given them credit for.

★★★Their research suggests that dogs’ barks have evolved into a relatively
sophisticated way of communicating with humans. To see if humans can
interpret what dogs mean when they bark, researchers played human
volunteers 21 recordings of barking dogs. ★★★

The recordings captured dogs in seven situations, such as playing with other
dogs, anticipating food, and encountering an intruder. The people showed
strong agreement about the emotional meaning of the various barks,
regardless of whether they owned a dog or not. They were also equally
successful at guessing the situation that had provoked the barks.
http://www.gakushuin.ac.jp/univ/adm/adm/test/ippan/06/q/3e.pdf