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This is what it sounds like when giraffes hum to each other at night

The giraffe is not as silent as previously assumed. (EPA/Roland Weihrauch)

Did you know that giraffes hum to each other? No, of course you didn't, so stop pretending you did.

In fact, researchers have only recently identified the illusive giraffe hum, New Scientist reports. And it sounds like this:

Until now, scientists thought that giraffes were either totally silent (save for some snorting noises) or that they made sounds too deep for humans to hear.

WIRED points out that giraffes have all the equipment one would need to make audible noises -- physically, their vocal muscles are quite similar to a horse's -- but it seemed like they just didn't bother.

[Watch as opera singer performs throughout his own brain surgery]

But after analyzing almost 1,000 hours of sound, the researchers were surprised to find that giraffes did make noise in the audible range. It was just on the really, really low end of it. And the humming, which was quite quiet, only took place at night.

Because the researchers only listened to isolated sound, they can't really say much about what the vocalizations might be for. They don't know what the giraffes were doing when they made these hums -- if they were soothing their young, signaling danger, or just keeping tabs on each other -- so for now the humming is pretty mysterious. To figure out what the droning is for, researchers will have to catch hummers in the act.

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