And Moses stretched forth his rod toward heaven: and the LORD sent thunder and hail, and the fire ran along upon the ground; and the LORD rained hail upon the land of Egypt. The Lord sent thunder - קלת koloth, voices; but loud, repeated peals of thunder are meant.
And the fire ran along upon the ground - ותהלך אש ארצה vattihalac esh aretsah, and the fire walked upon the earth. It was not a sudden flash of lightning, but a devouring fire, walking through every part, destroying both animals and vegetables; and its progress was irresistible.