If anything, a serpent is rather flexible and ready to stretch, which her body was ready and able to do even if his shape and size weren't within 'human' proportions. Even if he were bigger than most, that just meant being able to push him through the soft entrance into the oviduct for a deeper penetration. In fact, Jisu sunk onto him as much as one could in a single motion, eliciting a gasped moan, nearly sounding like "more" from his own fangs on her neck. She even eased her head back to expose and offer more of her neck to whatever marks and bites may happen.

In a lot of ways, it just pinged into the feral beast part of her brain. As Jisu pulled herself up to ride into him, her nails scraped and dug into his shoulder and rib cage, not to necessarily draw blood, but certainly leave some lingering marks of her own.