Why do turtles sweat on their backs in rainy days?

Before the rain, the water vapor in the air tends to be saturated, and the turtle's back is cold, because when it is cold, the water vapor condenses into small drops on the turtle's back, which looks like sweating. So people will see the illusion that "the tortoise will sweat on its back". The turtle's back shell is wet, the lines on the shell are mixed and the color is dark, which is a sign of rain; If the humidity is light (less water droplets), the probability of rain is about 50%, and if the humidity is serious (more water droplets), the probability of rain is about 90%.

Because the tortoise sticks to the ground, its back is smooth and cool. When warm and humid air comes, saturated water vapor will cool and condense on the cool turtle's back, and it will rain. If the air is dry, it won't rain. Therefore, the tortoise can also be a "weather forecast".