The Traveling Dust and the Boils Wet Without and Dry Within

"And it shall become dust over all the land of Egypt" (Exodus 9:9). Here is an argument from the lighter to the weightier: if dust, whose way is not to travel, traveled a journey of forty [days], how much more so a sound, whose way is to travel. This is what is written: "And they journeyed from Rameses to Succoth" (Exodus 12:37), a journey of sixty [other version: a hundred and twenty] mil, a journey of thirty parasangs - and the voice of Moses traveled a journey of forty days, to fulfill what is said, "And I bore you on eagles' wings" (Exodus 19:4). "And there was a boil breaking out in blisters" (Exodus 9:10). Rabbi Joshua ben Levi said: the boil that the Holy One, blessed be He, brought upon the Egyptians was moist on the outside and dry on the inside, as it is said, "And there was a boil of blisters breaking out on man and on beast" (Exodus 9:10).