Lacy and Rose have been playing on the swingset. I've been watching them do "tricks" on the slide. Lacy wanted Rose to slide down on her tummy, so she yelled out for her to do so. "Go down on your tummy, Rose!"
So, she slid down, lifting up her dress to expose her tummy. When Lacy kept insisting she go down on her tummy, Rose got confused and stuck out her tongue. Lacy kept telling her, "Go down on your tummy!" so eventually Rose stuck out her tongue while exposing her tummy.
She understands basic English, just not the finer points.