Conceal SpellSource Ultimate Intrigue pg. 80
You can hide the evidence of spells you cast.
Prerequisites: Deceitful, Bluff 1 rank, Disguise 1 rank, Sleight of Hand 1 rank.
Benefit: When you cast a spell or use a spell-like ability, you can attempt to conceal verbal and somatic components among other speech and gestures, and to conceal the manifestation of casting the spell, so others don’t realize you’re casting a spell or using a spell-like ability until it is too late. The attempt to hide the spell slows your casting slightly, such that spells that normally take a standard action to cast now take a full-round action, and spells that normally take longer than a standard action take twice as long. (Swift action spells still take a swift action.) To discover your ruse, a creature must succeed at a Perception, Sense Motive, or Spellcraft check (the creature receives an automatic check with whichever of those skills has the highest bonus) against a DC equal to 15 + your number of ranks in Bluff or Disguise (whichever is higher) + your Charisma modifier; the creature gains a bonus on its check equal to the level of the spell or spelllike ability you are concealing.
If your spell has a somatic component, any creature that can see you receives a Perception or Spellcraft check (whichever has the highest bonus) against a DC equal to 15 + your number of ranks in Sleight of Hand + your Dexterity modifier; the creature gains a bonus on its check equal to the level of the spell or spell-like ability you are concealing. Since you are concealing the spell’s manifestation through other actions, others observing you realize you’re doing something, even if they don’t realize you’re casting a spell. If there is a verbal component, they still hear your loud, clear voice but don’t notice the spell woven within. If an opponent fails its check, your casting also does not provoke attacks of opportunity, and an opponent that fails its check can’t use readied actions that depend on realizing that you’re casting a spell or using a spell-like ability, or readied actions such as counterspelling that require identifying the spell you’re casting. Spells such as fireball that create an additional obvious effect (aside from the manifestation of casting that all spells and spell-like abilities share) still create that effect, though it might not be obvious who cast the spell unless it emanates from you.
If a character interacts with you long enough to attempt a Sense Motive check without realizing you have been casting spells, that character can use Sense Motive to gain a hunch that you’re behaving unusually.