Encourage it further

Jessica's eyes slipped to the moon, her hidden source of strength this night. A black plan entering her mind. If lust would sate these beasts, and it was not her life they wanted, then she could survive yet.
Jessica obediently opened her lips to the beast, and it was all she could do to try to not gag (and fail) as the beast thrust into the back of her throat. It was covered in a musky mucus that tasted of earth and nothing too foul. The beast paid no heed to her comfort still, as it began its own sawing rhythm.
With that beast preoccupied, Jessica ground her hips against the member in her quim, driving the cock deeper into her, and despite her intentions of ending it quickly, felt the beginnings of heat at core growing.
Instinctively she brought her one free hand to the cock in her mouth, making a tight circle for it to thrust into, and control the banging her head was receiving. The beast continued its pace unabated, but the technique worked, she felt the cock grow even larger in her mouth. The sensation of pumping through her hands mirroring the motion between her legs.

Unexpectedly, the Dead Crawling Thing laying on her, pressed its mouth into her breast, almost suckling, causing an unwelcome surge of heat to blossom from her chest. Its thrusts a metronome of sensation from her hips. Jessica again surprised herself, the pleasure causing her to apply suction to the cock in her mouth, cause a flutter of contraction in her crevice, as if to draw the cock deeper.
This proved too much to the beast who had claimed her mouth, it abruptly surged in her mouth, flooding her mouth with its cold thin jism, which went down her throat a little much to Jessica's disgust before she could react. But she quickly used her hand to pull it from her lips, and pumped the remainder as far from her face as she could help. The thing continued to cum for many long seconds, Jessica had kept her eyes shut, but she could feel the liquid pumps of the cock through her hand all the same, aiming it away as best she could.
Most absurdly, after it came, the beast fell backward in a splash, all strength leaving its body after an apparently thunderous orgasm, expect for its slowly wilting cock sinking under the murk. Freeing Jessica's arms, leaving only one beast pinning her to the rock. Clinging to her like a desperate lover, the pace of its cock within her pushing her to cliff of pleasure she wasn't sure she wanted to cross.