In this short article about snails and weather, from what phenomena did the author discover that snails can predict the weather?

2 Wind temperature, humidity, dryness and cold; frontal cloud and rain belt; air pressure level; wind direction 3. "Generally speaking" indicates that the rainfall that starts in the northeasterly wind lasts for a long time and the rainfall is heavy, but in this case It’s not absolute, it reflects the accuracy and rigor of the language of scientific and technical literature. 4. It is suitable for travel, because the farther the wind direction is to the northwest, the stronger the wind and the faster the weather will clear up. 5. Example 1: The east wind blows after the rain, and the rain will not stop in the future. Example 2: The northwest wind often blows, and the weather is sunny today.