What is Occlumency?
1.
The ability to close off your mind from outsiders so that nobody knows what you're really up to or whose side you're on. Men have to train rigorously for this (Severus Snape and Harry Potter being examples of this), whereas women have it built into them naturally.
Occlumency: the reason why most men never see it coming when their girlfriend dumps them.
Severus Snape managed to fool even Voldie until the very end, doing incomparable damage to the Death Eaters' cause.
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