"Merlin this is Devils snare." Hermione clearly recognised what that meant as she leapt up and struggled towards a damp wall. She had to struggle because the moment she had landed the plant had started to twist snake-like tendrils around her ankles. As for Harry and Ron, their legs had already been bound tightly in long creepers without their noticing and it had almost reached their chest. Dean and Seamus weren't as badly tied down by it as it had only wrapped around their legs.