The next day Tiffany remembers to check her trap.

The next morning Tiffany is feeling a lot of emotions. She is feeling joy, excitement, restlessness, anxiety, and shame. She stays in her room longer than usual trying to get a hold of her nerves. Tiff feels that she would immediately die if anyone looked at her after what she did last night.

But suddenly, she remembers the trap she had placed in the bathroom. Her coffee cup with her jizz from yesterday’s wank session. It’s definitely dry by now, but she should really see if anything happened to it.

Tiffany quickly leaves her room and dashes into the bathroom. There she sees her cup on the counter next to the toilet right where she left it. She takes the cup and sees that it’s empty! Did someone dump it? Or perhaps even drink it?!

“Good morning, Tiff!” Says a cheery voice coming from the entrance behind her. Tiffany jumps and shrieks in sheer terror. She turns around to see Sophia beaming brightly at her.

“Don’t sneak up on me like that!” Tiffany exclaims catching her breath.

“Sorry about that Tiff. I’ll be more careful,” says Sophia.

Tiff shows her cup to Sophia. “Look Sophie! I spooged into this cup yesterday and left if here to see if it would have an effect on anyone. And now it’s empty! Not a speck of dry cum! Do you think someone took it?!” Tiff frantically explains.

“Oh, sorry! That was me,” Sophia replies. “I found it while I was getting ready for my date yesterday, and I just had to have it!”

Tiffany becomes stone-faced and stares into the void. Then she slaps her forehead. She feels incredibly stupid not having realized how easy it was for Sophia to have found the cup before anyone else.

“Huhh, I should have known. I guess I’ll just try again,” says Tiffany looking at her cup.

“Ooh, can I help?” Sophia eagerly asks. Tiff is startled but recovers quickly. She closes the door.

“Fine. You have to make up for this anyway. No one else is here, right?” she asks her older sister.

“Right. Mom and Emi are out right now. Saturday shopping and such,” replies Sophia.

Tiffany pops her cock out of her pajama boxers. Sophia stands to her right and grabs Tiff’s already hard dick. She strokes it at a steady pace and Tiff positions her cup ready to catch her cum. Then, suddenly…

“Ahhh! Whoa!” Tiffany squeals.

“Just thought I’d speed you up a bit,” Sophia says going under Tiff’s shirt and groping her tit.

Sophia kneads her little sister’s soft breast with one hand and plays with her little sister’s hard cock in the other. She slides her hand up and down the shaft and rolls her palm over the tip coating everything in pre-cum. She firmly squeezes Tiff’s boob and teases the nipple.

Then Sophia starts kissing Tiffany’s neck. She pecks and sucks at Tiff’s supple skin coating her neck with saliva. Tiffany can’t help but moan loudly. In no time she is ready to cum.

“Hhhaaaa!” Tiff groans as she ejaculates into her coffee cup. After a good night’s rest, she is easily able to fill the cup to the brim.

“Oh my! That’s pretty impressive!” Sophia exclaims. “Could I have just a bit Tiffy?”

“You already ruined by first experiment Sophie. I don’t need you ruining another one!” scolds Tiffany.

“Pleeeaasee?” Sophie begs sweetly.