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Free actions don’t take any time at all, though there may be limits to the number of free actions you can perform in a turn. Free actions rarely incur attacks of opportunity. Some common free actions are described below.
Drop an Item
Dropping an item in your space or into an adjacent square is a free action.
Dropping to a prone position in your space is a free action.
In general, speaking is a free action that you can perform even when it isn’t your turn. Speaking more than few sentences is generally beyond the limit of a free action.
Cease Concentration on Spell
You can stop concentrating on an active spell as a free action.
Cast a Quickened Spell
You can cast a quickened spell (see the Quicken Spell feat) or any spell whose casting time is designated as a free action as a free action. Only one such spell can be cast in any round, and such spells don’t count toward your normal limit of one spell per round. Casting a spell with a casting time of a free action doesn’t incur an attack of opportunity.