Question: In Lockharts classroom, Hermione shouts "Imobulous" or something like it and all the pixies are frozen in mid air and can't move. Why don't Ron and Harry just use the same spell on the spiders when the spiders start to come after them?
Xofer
3rd Apr 2004
Answer: They're panicking and can't remember the spell. Hermione is the smarter and more level headed of the three, that's why she remembered it.
Xofer