1)
Why, by this plague and all the subsequent plagues, did Hashem always say "Machar"?
2)
Why didn't Par'oh's Chachamim not try to replicate Arov?
1.
Riva (7:11): Par'oh did not call them, for he already saw from lice that the magicians could not do so.
2.
Moshav Zekenim (12): The magicians saw from lice that it was all from Hashem, and their actions will not help; it is a waste of effort.