Have one fellow standing, holding an unopened pop bottle, the next holding a bottle opener (or stands ready to open the container, one hand as if holding the container and the other hand raised over it), the other two doing nothing. The first guy examines the bottle real close and passes it to the third guy, who guzzles it, pretends or for real, and passes the empty container to the last guy. This guy looks at the empty bottle or container with a sick look on his face and then burps as loudly as he can.