1)
Why does the Pasuk refer to the snakes as "ha'Nechashim ha'Serafim"?
1.
Rashi: Because they were venomous snakes 1 (that leave a burning sensation when they bite).
2.
Refer to 21:8:151:1 & 2 and notes.
1
See Sifsei Chachamim.
2)
Why did Hashem punish them specifically with a plague of snakes?
1.
Rashi: Let the snake, which was punished for speaking Lashon ha'Ra (about Hashem), 1 come and kill those who spoke Lashon ha'Ra (about Hashem)! 2 Let the snake, whose food all tastes like earth 3 come and punish those ingrates, whose one food can change to taste like any kind of food - yet they complain!
