To play with ants on the floor without knowing what is happening in one’s heart means: to describe a person sitting on the ground observing ants but unable to understand their inner thoughts or conditions. In this metaphor, ants represent small and incomprehensible things or individuals, while people represent thinkers or observers. It implies that when people face some small and trivial things or problems, they cannot truly understand the meaning or connotation. This sentence can also be extended to mean that people have limited understanding of complex issues or situations and cannot fully understand the details and deep meanings. It reminds people to face their own understanding of the world with humility and not to jump to conclusions easily, because we are just like "ants playing on the floor" and cannot penetrate into the true state of our hearts. "Playing with ants on the floor, wondering what's going on in my heart" is an expression in poetry or literary works, which has metaphorical and symbolic meanings.