One method of carbonating homebrew is to "prime" the fermented beer with additional malt sugars and then bottle it. Yeast that is still in suspension continues to ferment the beer and produces the CO2 for carbonation. The only downside to this method is that as the beer matures a cake of spent yeast will settle in the bottom of the bottle. While drinking this yeast is not harmful it can detract from the aroma, flavor and mouthfeel of the beer. It has also been reported that drinking this yeast can have a laxative effect on some people's systems. So, when serving my homebrew to friends who are used to grabbing a beer and drinking directly from bottle I always give the same speech about pouring carefully, leaving about a quarter inch of beer in the bottle as you pour, etc. After the first dozen or so iterations of this speech I finally created the sign you see below. I laminated a copy and taped it to my cooler.