Harry Potter and the Prisoner of Azkaban

So, you know how harry potter gets hit in the back of the head by hermione when she goes back in time, and how harry gets saved by himself with the huge patronus? if they could see all that, how come they saw buckbeak get executed, but it was changed in time?
i didn't phrase that very well....

Alex Rider-Point Blanc


If the evil guy clones himself and impersonates rich kids, can't the parents tell if his blood type is different?
yea....