The Pensieve
Snape proved that he was loyal to the good side all along, by passing his memories on for Harry to read in the pensieve as he died.
Too bad the pensieve is only fictional. Even if there was a machine that can read our memories, it would not be a machine that can tell us what really happened it the past. It will only tell what we remembered happen.
Same event, 2 different memories, a million different feelings.
