2. They click when they walk.
reindeer
There is a tendon in the front legs of caribou that snaps when they walk, making a click that can be heard from 30 feet away. Scientists believe this is a trait developed by the male to signal to other males just how big he is, and in fact, a study by a couple of Scandinavian fellows shows that the sound does correlate to the size of the animal. What I find curious about this, though, is that the study did not mention if the sound is present in female caribou or whether it matters to the ladies, who are not inclined to fight.
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