You can cast spells without observers noticing.
Prerequisites: Perform 9 ranks, bardic music.
Benefit: You can cast spells unobtrusively, mingling verbal and somatic components into your performances. To disguise a spell, make a Perform check as part of the action used to cast the spell. Onlookers must match or exceed your check result with a Spot check to detect that you’re casting a spell (your performance is obvious to everyone in the vicinity, but the fact that you are casting a spell isn’t). Unless the spell visibly emanates from you, or observers have some other means of determining its source, they don’t know where the effect came from.
A disguised spell can’t be identified with a Spellcraft check, even by someone who realizes you’re casting a spell. The act of casting still provokes attacks of opportunity as normal.
Source: Complete Adventurer, page 108.