Mark quickly removed his clothes, dropped to his knees behind Katy, and took over massaging the dildo in Katy's vagina. As the last vestiges of Katy's humanity were gone, Mark quickly removed the dildo, handing it to Cal, and thrust his own cock into Katy's slick canine pussy.
Cal watched Mark and his canine sister go at it for a few moments, and began to wonder what would happen if he used the dildo now. Cal sat on the floor, and slowly slid the dildo into his own canine vagina, and slowly began to thrust in and out. Watching Mark and Katy only served to heighten the feelings and throbbing building in Cal's body. Cal's thrusting of the dildo increased automatically, as he felt his body surge toward orgasm. The sight of Mark's body suddenly freeze, his knot ballooning inside his sister as he erupted in orgasm, sent Cal over the edge with his female orgasm crashing through his body. Cal leaned over to rest on his side, as he slowed the pace of his dildo thrusts, just fast enough to keep his orgasm in a slow churn.
Mark remained tied to Katy for a few minutes, and rewarded the female with generous petting of her soft fur. As Mark remained still, he felt a cold nose touch his naked ass. Buster, Katy and Cal's dog, was sniffing his ass. "I will give you a dose too." cooed a happy Mark to the large male dog. In Mark's mind, the desire to have sex with either gender was a normal as the desire to eat ice cream. Mark's knot began to shrink, and he gently pulled out of Katy. Mark slid over and allowed Buster to move up and sniff Katy's ass. Buster's cock quickly emerged, as Buster moved over Katy's back, and slid his cock into Katy's pussy, and began to thrust away. Mark moved behind Buster, and slid his cock under his tail, and pressed firmly into Buster's ass, and began to slowly increase the speed of his thrusts. Buster did not last long, as his knot expanded in Katy, and his thrusting stopped, while Mark continued to pound away at Buster's ass. A few moments later, Buster yelped a few times in pain as Mark's knot stretched Buster's ass, and Mark unloaded his cum into Buster.
As Cal watched the entire affair, he continued to work his body in the enduring orgasm from earlier. Cal felt left out, and slide the dildo as far as he could inside him, and crawled over to Mark. Cal reached between Mark and Buster and stroked Mark's large scrotum. Mark let out a low, moaning growl. Cal did the same for Buster. Both males remained fully engorged for a few more minutes thanks to help from Cal's talented fingers. Buster's knot shrunk first, and he pulled away from Katy. Mark grabbed Buster under his hind legs, "Not just yet." Mark, now recharged and ready to go again, began to thrust, slowly at first, then speeding up. Cal crawled over next to his sister, and began to pet her as they watched the two males go at it. Soon, Mark let out a growl while Buster gave a few yelps, and both were tied together by Mark's knot once more.
Cal asked, "So, you like a ass or pussy better?"
Mark held Buster tightly against his groin so Buster would not try to pull away. Hearing Cal's question, Mark gave a few pushes with his hips into Buster, "Right now, this tight ass is wonderful."
Cal removed the collar from Katy, allowing her body to resume human form. Cal crawled over to Buster, and put the collar around his neck. "As soon as your done, we can show Katy the human side of Buster." noted Cal.
Mark let out a low groan, and said, "Not just Katy, but all of us."