The Aquavirius Maggot supposedly is a creature that resembles a brain. While in the Department of Mysteries in the Ministry of Magic Luna Lovegood mistakably claimed that the pale blobs floating in the brain tank in the Department of Mysteries were actually Aquavirius Maggots though they were infact just brains. The Aquavirius Maggot is one of the many stange creatures that Luna Lovegood believes exists though not many others do.
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