You can quiet a target you grab.
Benefit: When you successfully initiate a grapple, you muffle sounds made by your target until it breaks the grapple. While the target is free to cry out (of fulfill the verbal components of spellcasting), you suppress the sounds so it is difficult for even nearby creatures to hear those noises. You may make a Stealth check against any opponent not directly observing you to prevent the sounds and movement of the grapple from being noticed.
Adventurer’s Handbook: Genius Guide Volume 1