“We must be miles under the school,” [Hermione] said.
“Lucky this plant thing’s here, really,” said Ron.
“Lucky!” shrieked Hermione. “Look at you both!”
She leapt up and struggled toward a damp wall. She had to struggle because the moment she landed, the plant had started to twist snakelike tendrils around her ankles. As for Harry and Ron, their legs had already been bound tightly in long creepers without their noticing.
The Trio’s fall through the trapdoor is broken by Professor Sprout’s protection for the Stone – Devil’s Snare.
So far, about the only thing we know about Professor Sprout (whom we have not yet met) is that she’s a “dumpy little witch” who teaches Herbology in the Greenhouses. With the Devil’s Snare, though, we at least meet her handiwork.
The brilliance of Sprout’s protection is that while the Devil’s Snare breaks the fall of those who go through the trapdoor, it also tries to kill them… and will succeed, unless the potential victim remembers how to fight it. If Harry’s and Ron’s reaction to their soft landing is any indication, most people would be lulled into a feeling of safety and might not even think to escape the plant’s tendrils until they are already being strangled or crushed to death. Worse yet, the more they struggle, the tighter the plant will bind them.
Devil’s Snare may not be as flashy as transfigured chess pieces, but it is truly an impressive bit of protection. In standard vampire fighting mode, fire or light will defeat the plant. But remembering that requires some knowledge of Herbology – and who but an Herbology geek would remember back to First Year Herbology lectures while they’re under attack from the plant?
Based on what we’ve seen of the Wizarding community, the average Wizard would most likely pay more attention to flashier subjects like DADA or Transfiguration or Charms, and wouldn’t stand a chance if attacked by Devil’s Snare – making it a doubly effective defense.
Thankfully the Trio have Hermione on hand to remember what Professor Sprout told them about the plant. And thankfully, they also have Ron on hand to remind her that she can conjure fire:
“Devil’s Snare, Devil’s Snare… what did Professor Sprout say? – it likes the dark and the damp – ”
“So light a fire!” Harry choked.
“Yes – of course – but there’s no wood!” Hermione cried, wringing her hands.
“HAVE YOU GONE MAD? Ron bellowed. “ARE YOU A WITCH OR NOT?”
“Oh right!” said Hermione, and she whipped out her wand, waved it, muttered something, and sent a jet of the same bluebell flames she had used on Snape at the plant. In a matter of seconds, the two boys felt it loosening its grip as it cringed away from the light and warmth.
And so the Trio escape the Devil’s Snare’s clutches.
But as with so many other elements introduced in PS/SS, this episode serves also to foreshadow later events. In OotP, a Devil’s Snare sent by a Death Eater as a “Christmas gift” to spell-damaged Unspeakable Broderick Bode successfully strangles the intended victim. And during the Battle of Hogwarts, Professor Sprout again uses Devil’s Snare – this time as part of the castle’s defenses against Voldemort’s minions.
Professor Sprout, Head of House for Hufflepuff, is also (as we can see) a formidable, if unconventional, fighter who who brings her less conventional resources as an Herbologist to bear in the battle against evil. Significantly, she will teach Neville Longbottom to do the same.