How do you gravity chug?

How do you chug a beer in one go? As far as I can see, there are two ways. First is fast chugging and the second is to gravity chug. The first one I can do but I struggle with the second one. When I searched on the internet everybody wrote things like “just open up your throat and let the gravity do the work”. That’s all good but HOW do you open up your throat? I’ve been trying and practicing for days now with no luck. The second the liquid comes in contact with my mount my throat closes. Any advice? Technique?