Exodus 8:5-6

And the LORD spake unto Moses, Say unto Aaron, Stretch forth thine hand with thy rod over the streams, over the rivers, and over the ponds, and cause frogs to come up upon the land of Egypt.

Stretch forth ... The miracle consisted in the reptiles leaving their marshes at the very time Aaron commanded them, as well as, on the assumption that they were Ranae Niloticae, in their leaving the waters and moist soils, and overspreading all parts of the country. The Hebrew word for frogs is in the singular, used collectively, and in the feminine gender.