Maybe this is old news by now, but these plastic beer cups fill from the bottom using a special draft machine.

So how does it work? Keep reading if you want me to spoil the magic.

Each cup has a magnet at the bottom which reacts with the machine. As the magnet touches the top of the machine and pressure is applied, beer begins to fill the bottom of the cup. Each machine is set to dispense a specific amount of beer, then stops. At that point, the cups can be removed from the machine and the magnet locks back in place to seal the bottom of the cup.

You can see the magnet in action around the :15 second mark of the video above. This specific magnet has the El Paso Chihuahuas logo on it, so you're looking for something slightly red in the middle of the cup.

Why is this better? Less foam! Notice how little foam goes into each cup as opposed to draft poured from a traditional spout.

Cool, right?