Well,i hope everyone remembers the movie.In the shreiking shack,when sirius was speaking about his dreadful life,snape arrives and shouts "expelliarmus" and sirius gets disarmed without getting blasted off.But after sometime when Snape points the wand at sirius and offers harry to jinx sirius(apparently),harry shouts "expelliarmus" and snape gets knocked off!!How can this be possible according to the books?I mean....a spell should have a same effect irrespctive of time is'nt it?On the contrary....in the novel,harry,ron and hermione disarm Snape at the same moment and as a result snape gets knocked off!!This is a noticable mistake from a HP book reader point of view!!Anyway,what did you guys think about this?