It looks as if a giant is sleeping just beneath the forest floor. Of course, giants don't exist, and even a hibernating underground bear couldn’t make the earth move as much as is shown in this video, which has been viewed almost 6 million times.

This mysterious phenomenon, which is usually described as some version of trees breathing—it always occurs in forested areas—actually has a meteorological (and geological) explanation.

“While it may look like this tree in the ground is breathing, that’s not exactly what is happening here,” meteorologist Erin Wenckstern explains on a Weather Network segment. “What we’re seeing is a pretty powerful windstorm, and it’s actually pushing the tree because its roots aren't really firmly cemented into the ground because of the dry soil.”

This can also occur because a tree or group of trees has grown in soil that sits on top of a layer of bedrock, so the tree roots aren’t able to dig deep into the earth to anchor it—leaving the roots to reach out horizontally (and shallowly) instead. Here's an example from Finland in 2011.

If you turn the sound on in any of these videos, you can hear the intense winds—and in some of them the camera scans to some treetops that are obviously being tossed around by storms. But without the full picture and the sound, it really looks like the tree—or the earth—is breathing.

"As I entered a patch of trees spared from clear cutting, I noticed the ground moving," Brian Nuttall, who filmed the first video, wrote in a Facebook post. "The punishing prevailing winds have taken their toll on the side hill, the roots have loosened and the mossy ground from the once shaded forest floor are giving way, soon to be toppled over."

Below, another example, this time from British Columbia in 2012.

Being near to the earth heaving like this is actually pretty dangerous. If the tree’s roots are moving this much, the tree could easily topple over with the next tough gust of wind. If you’ve ever noticed a tree that’s been blown over, you’ll see some roots still sticking into the ground and some that have been ripped up, often displacing a tremendous amount of earth around the base of the tree. But if the wind isn't strong enough, the trees will just sway above and rock the soil below—and live to take on another storm.