Artemis and her... traveling song?

Yes, you read right, Artemis (Art of Mischief) has a little tune that she foofs out whenever Ben picks her up. It's only for Ben too, which makes it even cuter. Before tonight I'd not heard it. But just a few minutes ago she started again. We've decided she's singing. It's so cute! We have no clue where this behavior comes from. It's the same melody most of the time, "do do-do do do-do do." Sometimes she'll change it up, it almost always seems to sound like video-game music. Surprise surprise in this household.