Telepathy

Telepathy is a passive ability that some monsters and PCs possess. It allows you to detect the exact position of any intelligent monster on the level. Intrinsic telepathy only works when you are blind. Extrinsic telepathy works on a limited range while unblind, and works completely while blind.

Acquiring telepathy
Intrinsic telepathy can be acquired by eating the corpse of telepathic monsters, eating an amulet of ESP, or polymorphing into a monster with telepathy

Extrinsic telepathy can be acquired by wearing an amulet of ESP or a helm of telepathy, or carrying certain artifacts.

Telepathic monsters

 * Floating eyes
 * Mind flayers
 * Master mind flayers

Pitfalls of telepathy
Mind flayers and master mind flayers can detect the location of PCs with telepathy, and attack them with a projectile attack ("A wave of psychic energy purs over you! It locks onto your telepathy!").

Unintelligent monsters can easily sneak up on and attack unsuspecting PCs while they are blind and using telepathy.