Just wanted to highlight one of Elie's points below from last week but on this week's פרשה:
י:ו וּמָלְאוּ הלמ"ד בשוא נע, לא לקרוא וּמָלוּ
It is not absolutely essential to use the שוא נע. However, one must be very careful not to skip the שוא altogether and pronounce it וּמָלוּ. Surely, the locusts were not circumcising the Egyptians houses.