The tingling sensation? Well, it's just carbonation. All those little bubbles are popping on my tongue, and it makes that fizzy tingling you feel.
Everyone has always assumed that was the case, but just recently researchers at the University of California did some experiments on this.
They treated half of the tongue on subjects with a substance that temporarily inactivates certain receptors. If the fizz came from purely mechanical stimulation, that is, popping bubbles, these folks should still have felt it. Instead, when they drank carbonated water they felt fizz only on the other side of the tongue.
But if it isn't the bubbles we feel, then what is it?
One idea is that pain receptors, called "nociceptors," are in fact the ones being stimulated. The theory is that enzymes in our mouths change the carbon dioxide in bubbles into carbonic acid, which stimulates nociceptors, and that's what gives that tingly feeling.