The smoke is created because of the change in pressure between the inside and outside of your mouth. The tongue clicking and breath holding heat and pressurize the air and water mixture in your mouth.
Here’s how you do it:
The resulting puff of smoke is what YouTuber Physics Girl has named the “Maculus Ridiculous” — because it makes you look ridiculous — cloud.
Then you hold your lips shut with your hands while trying to blow out to create pressure inside your mouth. This heats up the air even more, because as the pressure increases, so too does the temperature. And warmer air will hold more moisture — or water vapor — than cold air.
When you open your mouth and let the air out, the pressure and temperature of the air inside your mouth, plummets. As the humid air from your mouth cools down, it loses its ability to hold onto the water vapor, which condenses into tiny water droplets, just like a cloud.
First, you need to click your tongue to the roof of your mouth while it’s closed but full of air for 30 seconds. This creates tiny droplets of water in your mouth that, when they evaporate, create warm and humid air.
Then as you slowly open your mouth, a puff of “cloud smoke” billows out.
When a bunch of these droplets cluster together, they form clouds.
We usually imagine this process happening in the sky. But with a few tricks, you can replicate cloud formation in your mouth, no cold room needed.
This really works.