Question from a newbie: Taking memories out of your head?

[Dana Hoogland]

No: HPFGUIDX 164079

Hi I am new and I have a question. I have been reading many posts in
the archives and I have a question regarding the speculations
about "Snape's Worst Memory". I have seen many suggestions that
Snape removed these memories from his head to protect them from
being seen by Harry. Can anyone tell me why so many think that the
pensive is a memory elimination device? Although I have to admit
that I only read the series once I cannot remember seeing anywhere
that extracting the memory from ones head eliminates the memory from
the head itself. Slughorn's memory was still there even though it
was altered. In GoF Dumbledore talks about the memory Harry has seen
when strolling around in it and of course Snape knows perfectly well
what Harry has seen in his memory but that could not be if the
memory wasn't there in the first place. To be able to understand
what Harry has seen and what implications it would have shouldn't
both people have placed the memory back first before reacting to it?
If you have no recollection of it and if it can be used to be able
to control once emotions by removing the memory than why did Snape
react like he knows precisely what Harry has seen instead of only
being angry at Harry for putting his nose into other people's
business?

Doesn't Dumbledore state in GoF that it is a device to sort out the
memories to make better sence of them or to see if you might have
overlooked something? I never got the impression that putting the
memory into the pensive or store them into a bottle erases the
memory from your head or that it can be used to hide memories to
prevent anyone to see. Slughorn could have done that a long time ago
and there would have been no reason from him to alter the memory. He
could just have said the he lost it by removing it and throwing it
away. Also Snape explains in OotP that the mind is not an open book
so even if Harry was able to break through he would never be able to
see the entire memory, only flashes of it which would make less
sense to him than the pensive scene eventually did. Just my two
cents of course.

Dana