This is a test for an eventual, and hopefully better controlled, more polished series. Still its interesting. Here is the science:
Certain salts are hygroscopic, they will absorb water vapor from the air. Many salts are hygroscopic. A few are so good at pulling water out of the air that they will actually dissolve in this water and form a solution. The solutions themselves will continue absorbing water until equillibrium is achieved.
The subject of this video is Calcium Chloride, typically used as an ice melting agent or as a humectant on dusty roads. Its comes in round BB sized balls called "prills." CaCl2 is so efficient at absorbing water that at 90% relative humidity, it can absorb as much as 9x its weight is water!
In the video you see the initial "boring" phase where the dry prills are absorbing moisture and re-hydrating. Once the surface of the prills is hydrated they start to deliquesce, weeping a concentrated solution of the salt and water pulled from the air. The solution itself continues to pull moisture from the air as the prills dissolve. In this video the RH was about 65%.