Giraffes can make a number of different sounds, including hisses, growls, bellows, snorts, and bleats. For example, during mating season, a male will make a coughing sound, which lets the females know about his dating status. Females will issue a high-pitched whistle to keep their offspring in line. However, most of a giraffe's communication is nonverbal.
Among the best-known ways they communicate is by "necking" -- when two males will rub their necks together to establish which one is dominant. This can sometimes turn into a violent display in which the giraffes swing their necks at each other, but often ends with the giraffes caressing.
Giraffes will also use ultra low frequency vocal signals, called "infrasound," to warn others of danger, often over long distances. There is a lot that scientists do not yet understand about these mysterious vocalizations.
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