The door creaked open, and both of them froze. Then they saw it was just Andy's great dane Molly, who was surprised to see two new dogs in her owners' bathroom.
The confusing musks quickly got her in heat. The mix of Andy's scent and male dog scent from the one on her left was intoxicating, and she hastily turned around and moved her tail aside, showing off her soaked pussy to the two males.
"Oh fuck... does she want us to fuck her?" Greg asked surprisedly. He looked over at Andy, and saw his friend was transfixed by the sight of the animal that had been his dog presenting herself to him.
"Dude... is it OK if I do it instead of you?" Andy asked hazily. He didn't think he'd be able to stop himself even if Greg said no. To his relief, Greg nodded, and Andy stepped forward on all fours, moved his front paws around Molly and mounted her.
Molly panted excitedly as Andy's thick cock filled her up, and Andy quickly started pounding in and out of her forcefully, grunting at how good the tight slit around him felt to fuck. He ached to lodge himself inside her with his new knot, intoxicated by the unfamiliar feelings of horniness and Molly's strong feminine scent.
Behind the two mating animals, Greg was watching intently and masturbating his reshaped cock in one hand. His eyes drifted between Molly's hole being pounded forcefully by Andy, and Andy's butthole, which he imagined mounting once his friend was done with Molly.
Andy was quickly getting close, as he felt Molly's walls cling to him tighter, and his primal instincts reminded him that as Molly wasn't neutered, he would most likely be about to breed her. That realization pushed him over the edge, and he shot a huge load inside her, grunting as his knot engorged to trap him inside her for a few minutes.
And within Molly's womb, the reason she had cast aside any reservations and allowed herself to act on sexual instinct was surrounded. A torrent of seed took root in her several eggs, and soon all of them had been fertilized.