The Schlieren technique, achieved by refracting light on objects before a concave mirror, allows you to see things that would usually be invisible — like the heat of a fire, the cold of dry ice, or even a burp.
Here's what the heat of a lighter actually looks like...
And here's the chill of dry ice.
Here's what Isopropyl Alcohol looks like...
...And here's Helium.
When treated with the Schlieren technique, a burp isn't that gross anymore.