Snakes are cold-blooded animals that need to hibernate, typically waking up slowly after the start of spring thunder. Just after waking, the weather is still very cold, so even if they are awake, they won't move around much outside.
Now that the weather has warmed up, the snakes that survived hibernation have all come out, and it was easy for the Red Python to summon a non-venomous snake. However, snakes have their own territories.
At that time, a Bamboo Leaf Green Snake occupied that area, so it wasn't possible for any other non-venomous snakes to be around. The non-venomous snake that the Red Python was summoning was still on its way when the Bamboo Leaf Green Snake attacked someone, resulting in an accidental coincidence no one expected.
"So that's how it was, Little Red, I'm sorry!" Knowing that she had wronged the Red Python, Mo Yan stroked its head and apologized with shame.