To watch you two pleasure each other.

"Ooh...That's our third favorite thing to do together," you squeal, clapping your hands together.

One round of naked rock, paper, scissors later, you're leaning back against the headboard, gasping and breathing heavily, playing with your breasts, while your sister has her face buried between your legs. Paul is sitting on a chair across from you, idly massaging his cock over his shorts. Your lip quivers and your legs shake when Dahlia takes your mound in her mouth and licks all over it. "I'll never get tired of how good you taste sis," she purrs, rubbing your clit with her lips.

"Mmm...Yeah?" you pant, licking your lips. "Well come up here and let me taste it." Dahlia dives back down and slurps up your juices noisily, scooping up mouthfuls with her tongue. Being very careful not to spill a single drop, she kisses her way up to your face. You open your mouth wide and she lets the juice-spit mixture trickle out between her lips. The mixture is both sweet and salty, and she helps you mix it up even further by stirring it in your mouth with her tongue. Your tongues dance together and you slide your fingers into her pussy, coating them in her juices.

Without breaking the kiss, Dahlia does the same to you. You moan in each other's mouths as your fingers go to work. The two of you stare into each other's lust-filled eyes until your fingers are thoroughly drenched in the other sister's juices. You cheat and go for her sensitive spot, making her lose this round of your long standing "Who can cum last?" competition. She would complain, but she's too busy cumming her brains out to say anything.

Paul applauds the pair of you from his chair, his thick, turgid cock standing at full attention in appreciation. "If that's number three, ladies, I can't wait to see the other two."