Threatened Area

Threatened Area

To threaten an area, a creature must be capable of inflicting harm upon a foe in a legal fashion as a reactive action, namely, be able to take attacks of opportunity. Usually this requires a creature to be proficiently wielding a melee weapon or possess natural attacks. Ranged attacks almost never threaten squares, and if they do, require special abilities or feats to do so.

Creatures who can make legal attacks of opportunity threaten all spaces they have Reach to and all spaces they occupy. Yes, moving around inside the space of a hostile creature provokes attacks of opportunity, so be careful when seeking that internal flank.