So it stopped the centipede and told it its question. What did the first one refer to?

Frog?

A frog philosopher saw a centipede walking. It thought to itself, it’s troublesome enough for me to walk on four legs, so how does the centipede walk on so many legs? How does it know which foot walks first and which foot walks last? What happens next? Which foot? This is a question worth exploring. So the frog stopped the centipede and told it his question. After hearing this, the centipede was stunned and said: "I have been walking all my life, but I have never thought about this question. Now I have to think carefully before I can answer you." The centipede stood there for several minutes, thinking left and right. , looked at his leg, then looked at that leg, and suddenly, he found that he couldn't move. It held up precariously for a moment, then fell over. The centipede told the frog what he thought: "Please don't ask other centipedes the same question. I can no longer control my feet.