1. Some flying insects will fly near the water surface, and swallows will also fly low and stick to the water surface to hunt for food.
2. In the sultry summer, swallows fly low across the water surface, splashing water, cleaning their feathers and cooling themselves.
3. Because the wings of the small bugs it likes to eat are wetted by the sticky air when it rains, it can't fly high, so it has to fly low to catch them.
4. Swallows build their nests with mud in their mouths and water in their mouths.