Shut her up

Knowing your sister is listening, you quickly thrust your cock into the woman's mouth and grab her head.

"Mmmfff" is all you hear as you pump the woman's mouth, realizing you're about to cum, but you see the door handle turning slowly.

"Not now!" you shout at your sister as your orgasm hits, your cum flooding down the woman's throat, spilling out all over her chin and chest.

Quickly, you run to close and lock the door as the woman looks up at you...