Mind Flayers

Also called Illithid, the brain-devouring mind flayers are hideously alien creatures of the Underdark. Evil beyond redemption, they will consider you a slave — or simply food — if they consider you at all.

I have heard these monsters will suck the brain right from a person's head!

— Volo

Then, Volo, you should be safe enough.

— Elminster

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Source: bg2ee/original_manuals/baldurs_gate_2_ee_amn_survival_guide.pdf — "Some Monsters of the Sword Coast" → "Mind Flayers".