Put me in the sous vide camp, too! But, if you don't have that tool in your tool box, then quick grill, as others have suggested.
This is a real thing! Be Careful. I've experienced it first hand on a BGE. It happens when you have a big fire going (500F+) and quickly starve it for air by shutting down all the vents. Combustible gases build up inside and if you open the lid right afterwards (before the fire is out), oxygen rushes in and you get a big fire ball. The best way to mitigate this is to crack open the top vent first, to let the gases vent out, then open the main lid. If you have any doubts about this, the Naked Whiz did a video on it.
http://www.nakedwhiz.com/flash.htm