Zero

(Sera's learning some basic math - I'm able to ask what 3 + 2 is, she'll hold up three fingers on one hand, two fingers on the other and come up with five as the answer. Today, I was seeing if she understood the concept of zero.)
Me: "Sera, if you start out with zero fingers (I held up a fist), and add two fingers (I held up two fingers on my other hand), how many fingers do you have?"
Sera: "Two!"
Me: "That's right! If I start out with zero apples in my basket and add five, how many do I have?"
Sera: "Five!"
Me: "Good! If I start out with zero dogs in the room, and bring in twelve dogs, how many dogs do I have?"
Sera: "Lots!"