The second plague was the plague of frogs (8:2). The Egyptians gave special honor to amphibians such as frogs. These animals can live both in water and on land. Because of this, Egyptians connected them with life and survival. Egyptians were very concerned about life after death.
Through this plague, God showed that frogs do not control life. They do not have special power over survival.
Some people suggest that this plague happened naturally after the Nile River became unfit for life. However, the size and intensity of the plague were far greater than what would normally happen in nature.