Curiouser and Curiouser

I drink a lot of flavored carbonated water these days: about a quart a day. So naturally, the point came where I read the nutrition information on the bottle. There are three servings per bottle. One serving is zero calories, while a full bottle has ten calories. 

Now, I'm no math whiz. But shouldn't that mean that there's just over three calories per serving? Or do the calories magically develop once you've had the last swig of the bottle?

Can we transfer this science to, say, cake? Unless I eat the whole cake there aren't any calories? Sure would make dieting easier. And more fun.