From the way Robert was acting, Carla knew something was going to happen, but she wasn't prepared in the slightest when his cock suddenly filled her mouth with his juice. Although she was startled by it, she had enough presence of mind to keep going while quickly evaluating the semen he kept squirting.
Even though she wasn't wild about the consistency or taste of it, she expected that was mostly due to having never tasted it before. After she had the time to get used to it, she decided that it really wasn't all that bad, and didn't have any qualms about swallowing it as she'd been told to. By the time his cock had stopped pulsing in her mouth, she'd actually started to kind of like the taste of her brother's cum, and surreptitiously used her lips to milk his shrinking shaft of any remaining drops as she slowly pulled her head back before letting him slip from her mouth. As she moved to stand up again, she proved she'd done what she was supposed to by saying "There, I did it", only to hear the man with the gun say "You sure did, missy!", with a brief laugh.
When asked "That was pretty good, wasn't it, kid?", Robert was ashamed by his enthusiastic "Yeah!"
"Well, the next part don't feel as good, but it's almost as fun", the armed man said. Directing himself to Carla, he said "Okay, missy, time for you to sit down and spread 'em so Junior can get his licks in!", drawing laughter from the two men behind him. Despite feeling herself blushing, Carla tried as best she could to maintain her composure as she sat down in one of the armchairs and moved her legs apart- only to be told "Nah, not like that. Scoot forward so your ass is on the edge and hang your legs over the arms. You don't want your brother gettin' a crick in his neck, do ya?"
It was only a few moments until Carla was positioned to the man's satisfaction, causing her to blush even harder at knowing the sight she presented to everybody.
Seeing that his sister was ready, Robert wasn't surprised when the man told him "Go on, kid. Get your face in there and find out what fresh young pussy tastes like. Trust me, it's good!"
After moving in front of the chair Carla was in, Robert moved to sit on the floor; as low as the chair was, he knew he wouldn't be comfortable kneeling, and he suspected he was going to be there for a while. Though he didn't know it, Robert's attitude closely matched his sister's: as much as he hated being forced to do things with his own sibling, there was also part of him that welcomed the chance to learn and do things he'd heard of and wondered about.
With his head that close to Carla's exposed pelvis and crotch, the young man had the opportunity to get his first good look at the details of female genitalia-and found them lovely, to his surprise. Carla's bush wasn't as large or thick as his, making it possible for him to see the surface of her mons; with her sitting the way she was, he didn't have any trouble identifying the small bump at the top of her slightly parted cleft as being her clitoris. Flowing down from it were her inner lips, thin and small and looking incredibly soft. At the bottom, between them, he could see the entrance to her vagina; with her legs spread the way they were, she was opened up enough for him to make out what looked like a small ring inside her. Thinking back to some of the diagrams he'd seen, it took him only a moment to understand that that ring was her hymen… the maidenhead that defined her virginity. The entire area around her opening looked shiny to him, though he didn't know the significance of it until he heard one of the other men exclaim "Hey, it looks like missy's already worked up a little bit!"
Recalling the disappointment he'd seen on Carla's face (and what she'd done after he'd cum in her mouth), it dawned on Robert that his sister might be glad about what they were doing the same way (and for the same reasons) he was. Awakened to the possibility that Carla wasn't a completely unwilling participant, the young man silently resolved to do as much for her as she'd done for him.
After mentally reviewing the little bit of factual information he had about cunnilingus, he leaned forward; when his head got close to his sister's pelvis, he got his first whiff of a singularly enticing aroma. After a couple of seconds, he understood that what he was smelling was the liquid that was making Carla's opening and labia shine. Knowing that it was the scent of her arousal only added to the appeal of its slightly musky and somehow sweet overtones, and made him eager to find out if her juices tasted as good as they smelled.
Extending his tongue, he drew the end of it across her opening and got his first taste of essence of emale-and fell in love with it. Carla's taste wasn't exactly the same as the smell, it was somehow better. He repeated his actions, and extended them by drawing his tongue up between his sister's labia for a little ways. Another pass of his tongue ended only after he'd made careful contact with her clitoris, which drew a soft noise of pleasure from her. Robert didn't think anyone else could see what had happened, but he'd felt Carla lifting herself up slightly to increase the contact between his tongue and her pussy… something that told him she liked what he was doing.
Carla had felt mixed emotions as she'd watched Robert's face approaching her pelvis. That she'd finally find out if having her pussy "eaten" was as good as it sounded like it would had her feeling eager anticipation, while she was deathly afraid that her brother wouldn't find her taste and smell as appealing as she did. Much to her relief, his reaction after his tongue touched her the first time was enough to reassure her that she wasn't gross or disgusting there. When he'd progressed to touching her clitoris with his tongue, she couldn't help trying to increase the pressure at least a little bit. She hadn't been masturbating that long, but she'd definitely learned how much pressure felt best to her.
Though she hadn't meant it as a signal, Carla knew that Robert had noticed what she'd done when his next contact with her clit was firmer than the first; since the second wasn't as firm as she liked, she tried pressing herself up again. It apparently worked, because when Robert began using his tongue on her clit again, it was nearly perfect. Between what he was doing to and with her clitoris, and the way he was using his tongue at the entrance to her vagina, Carla was receiving more and better stimulation from Robert than she'd ever managed to give herself.
Robert had been worried that he wasn't pleasing Carla when he felt her press herself up against his tongue a second time, but she didn't do it again; when he realized that she was beginning to get even wetter than she'd been before, his fears were completely assuaged, leaving him free to enjoy what he was doing. The taste of his sister was a treat for Robert's taste buds, and knowing that he was arousing her just by using his mouth on her left him feeling rather pleased with himself. It wasn't long until he was totally focused on what he was doing between his sister's thighs.
Vic and Ellen had both watched the initial intimacy between their kids with horror and anguish, but as it had progressed, their reactions had gradually changed.
As he'd watched Robert's actions with his sister, Vic had gone from outrage at what his daughter was going through to consoling himself that at least Robert wasn't doing anything to hurt Carla. But the longer he stood there looking at his nude daughter, the more insistent the little voice in his head telling him how pretty she was became. Then the damn thing started pointing out how sexy she looked, and how she was responding to what her brother was doing to her-pointing out things that he'd willfully ignored: the faint flush she'd developed, how the ends of her breasts had erected and how hard her nipples had gotten, how willingly she'd sucked her brother's cock, and then how wet she was even before Robert started using his mouth on her. His reluctant awareness of her as a sexual being, grown and developed enough to engage in (and plainly enjoy!) the things their captors were having her do, combined with the sight of her lithe naked body to have him starting to feel a vague desire… the target of which he was unwilling to examine too closely.