What is the significance of the fact that Pharaoh was the first to rise at midnight?
Rashi: He was the first to rise and go round the houses of his servants to arouse them and inform them of the calamity that had befallen them. 1
See Sifsei Chachamim.
Surely there were houses in which the Bechor had already died! How can it be that there was no house without a Mes?
Rashi: If there was no firstborn in the house, then the oldest member of the family died. 1
Da'as Zekenim #1, Hadar Zekenim #1, from Sifri: Their custom was, when a Bechor died, they made an image of him. Those images melted, and it was as harsh for them as the day of death.
Da'as Zekenim #2, Hadar Zekenim #2: Mice dug up the firstborns from where they were buried and dragged them [to the houses].
Rosh: The Egyptians buried their dead in their houses, and dogs dug up the corpses and dragged them from house to house.
And we find the word firstborn used in this way in Tehilim (Tehilim, 89:28 [Rashi]).
