Stan was in the corner of their cage. Cursing to himself as sandy was in heat again. Theyve been able to resist their urges the first time it happened. But this year its stronger. Sandy sat on the opposite side of the cage paws soaked in juices as she was masturbating heavily. She groans in frustration as she sparays her paw upon cumming but it just makes her heat worse. Her body demanding she finds a male to breed her but the only one available is her own brother. Last years was bad enough but this one feels even worse. Its only the second day of it and shes already at her limit. Stan lets out a gasp as he shoots his load on the floor. Sandys heat has left him aroused all day. As much as he hates seeing her miserable he knows theres nothing he can do besides breeding her. But such a thing is wrong as shes his sister. The more their rational sides struggle with the problem the more their primal side grows telling them to give in to instincts. Sandy was the first to give in. she gets up and heads towards stan. Stan lets out a suprised gasp when he feels sandy hugging him from behind. She reaches around and strokes his erect cock pre drippin on her paws. Her scent overpowers him from the closeness. His mind driven by her heat gives in. He grabs her face and embraces her in a deep and pasionate kiss. After breaking the kiss sandy turns around and gets on all fours raising her backend to him with pleading look in her eyes. Stan grabs her hips and guides his member to her virgin hole. With a nod from sandy stan pushes in. hen he reaches her hymen sandy pushes her hips back shoving him past her hymen breaking it. Sandy was to far in heat to feel any pain only pleasure from having a male finaly inside her. Stan tightens his grip on her hips and starts a slow rythm. Both panting and moaning each others name. The cage is filled with the sounds of their mating. Soon stan hits her g spot causing her to cry out in pleasure asn she cums. Thanks to her orgasm soaking his member stan is able to speed up his hips now a blur. Stans mind filled with lust and desire to impregnate the fertile female beneath him. Feeling him starting to shoot pre sandy begs stan to cum inside to sate her heat and fill her with his babies. Hearing her beg stan leans down and bites her neck as he focuses on getting as deep as he can. Feeling him bite her neck sends her off again her cunt tightening around him like a vice. Stan lets out a growl as he reaches his peek. Millions of ham ham sperm comes pouring into his sisters fertile womb eager to knock her up. Sandy sighs as the warm cum exstinguished the burning heat in her belly. She thanks him for helping her.  Satisfied sandy passes out on the floor. Stan soon falls asleep on her back still connected to each other dreaming about their future. Meanwhile deep within her womb two eggs were found by his seed and were quickly fertilized. We can only hope the new twins dont copy there parents.