Solomon dropped his pack. This little copse of grass would do to rest for the night. Green and soft - better than that rocky camp last night. He kicked aside a desiccated dear corpse mounded in the center of the grass. He wasn't about to share a bed with that. Solomon threw down his bedroll, took a nip from his flask, and shut his eyes...
The sun hit his eyes. Groggy, he realized he'd slept past the dawn. He felt numb, his limbs heavy... He'd only had one nip... Feebly, he tried to sit up, only to find himself bound to the ground. Farkin' pixies! No, that wasn't right. His vision cleared, and he saw in horror that his skin had been pierced and threaded with countless blades of grass! Solomon struggled, feebly, feeling drained, as the sun continued to rise. He vaguely felt the grass pierce more fully into his body and wrap more securely around his limbs...
One of many banes of the unwary in the wilderness, Carnivorous Grass presents a tempting "bed" of thick, soft turf for a weary traveler or animal to rest upon. The grass may give itself away by one or more desiccated corpses within its bounds, although the age of the corpse may not be clear, as the grass' attack and consumption of victims accelerates any apparent decay.
Only after they slumber, will the grass present its true nature, working its way through bedding and clothing to pierce the flesh and bind the victim to the ground as it slowly drains them of lifeblood and strength.
The grass manages this feat by producing an anesthetic effect (save vs poison to detect/be awakened). If awakened, the victim may escape with little difficulty, tearing away the grass blades from their flesh. Extracting oneself will cause 1d4 damage.
Those who do not awaken will take 1d6 damage +1d4 STR drain (One "attack" per night, three "attacks" per day). A trapped individual must make a STR test upon awakening to escape the entwining and piercing grass. They may make an additional attempt after each grass "attack," but repeated failures will lead to decreasing chances of escape as their blood and strength are drained.
(AC: Umm, it's grass. HD: No matter what you do to it, it's eventually growing back...)
And of course there's real "carnivorous" grass (via symbiotic fungus, but who's counting?)