Invisible Spell

 
Prerequisite(s): Any Metamagic Feat
 
Benefit: You can modify any spell you can cast so that it carries no visible manifestation. All other aspects of the spell remain the same. This does not apply to the spell components (if any), and someone with Spellcraft will still know what spell you are casting. For example: A fireball altered by this feat will be invisible until the point of detonation. At that point there will be an explosion and items in the area of eefect will catch on fire, etc. A spell modified by this feat uses the normal level spell slot for the spell.
 
Source: Cityscape