Dora Bas Rivka Silver O'H
"You've Got to Get Lice Into Your Head!"
After Moshe and Aharon departed from Pharaoh, Moshe prayed to G-d about the frogs. G-d answered Moshe's prayers and the frogs died. The Egyptians shoveled them into huge heaps of stinking frog carcasses. But Pharaoh again steeled his resolve and refused to release the Jews.
And so, G-d told Moshe to have Aharon strike the dust of the earth with his staff; this would cause the dust to turn to lice. They did as G-d instructed and the Egyptians became infested with lice. Pharaoh's magicians were unable to replicate this feat, which they attributed to the metaphorical "finger of G-d." (We often speak of the "hand of G-d," but why did they here call it a finger? It could have been an attempt on the part of the magicians to minimize things, but the difference between a hand and a finger is that a finger pinpoints things.)
When Pharaoh did not respond to the third plague, G-d sent Moshe back again with a warning: let the Jews go or wild animals are coming. They will run rampant throughout the land, except for Goshen, where the Jews live.
(In the previous aliyah, Moshe did not personally strike the Nile to start the plague of blood because the river had protected him as a baby. Here, he does not himself strike the dust of the earth to trigger the plague of lice because it had protected him when he buried the Egyptian taskmaster in parshas Shemos. If Moshe shows such symbolic gratitude to inanimate objects, we should certainly be careful to treat other human beings properly! See Rashi on 7:19 and 8:12.)