This is a camera trick with a glass of ice tea. This is a very simple image known as a Schlieren, where you can very easily see the heat waves and shock waves coming off of the objects. The conditions are very specific to the ice tea used (Arizona Ice Tea with Raspberry). The sugars used (honey) have a specific reaction when shining light through them. This is also strengthened by the color of this ice tea. To simply explain it, its heat waves like you see in the street as a mirage, except these are much closer temperatures. These videos are used to look at heat and even aerodynamics. For example where heat escapes from a home.