"As his speech and mobility improved, Healer Strout encouraged Mr Bode to look after the plant himself, unaware that it was not an innocent Flitterbloom, but a cutting of Devil's Snare which, when touched by the convalescent Mr Bode, throttled him instantly."
-- The Daily Prophet (OP25)
Devil’s Snare is composed of a mass of soft, springy tendrils and vines that possess some sense of touch. Devil’s Snare uses its creepers and tendrils to ensnare anyone who touches it, binding their arms and legs and eventually choking them.
- The harder a person struggles against Devil's Snare, the more faster and more tightly it binds them; if they relax, it will not kill them as quickly. Devil's Snare prefers a dark, damp environment and shrinks away from fire, so a well-placed flame spell such as "bluebell flames" will drive it away from its victims (PS16).
- First year students at Hogwarts learn about Devil's Snare in Herbology classes.
- A cutting of Devil's Snare, passed off as a potted plant (Flitterbloom), was used to murder Broderick Bode in St. Mungo's (OP25).
- Devil's Snare is mentioned in the Rumours advert for the Toots, Shoots 'n' Roots radio program (JKR).
- Professor Sprout used Devil's Snare as a weapon against invading Death Eaters during the Battle of Hogwarts (DH30).
The Daily Prophet reported that the Devil's Snare "instantly" throttled Bode when he touched it (OP22, OP25); given what we know about Devil's Snare, is someone giving perjured testimony about the details of Bode's death? If there was a witness competent to testify to how Bode died, and if Devil's Snare typically takes as long to kill as it took in PS16 (longer, since this one was much smaller), then somebody's lying about the details of Bode's death.
In the film (PS/f), the Devil's Snare had somewhat different properties and was driven back by a bright sunlight spell. There are not bright sunlight spells in the Harry Potter universe, however, so this is one of many instances where the film is in error.
While the Devil's Snare in the Potter books is clearly a magical plant, the name is actually borrowed from a real and very poisonous plant, the Datura stramonium, also known by such diverse names as ditch weed, loco weed, devil's trumpet, and my personal favorite, devil's twinkie.