Muggles' Guide to Harry Potter/Magic/Venomous Tentacula

Overview
The Venomous Tentacula is a dark red and spiky plant that has long feelers that can reach out and capture prey. Professor Sprout cautions her second year class, "Watch out for the venomous tentacula, it's teething." (Note that in some British / Canadian editions of Harry Potter and the Chamber of Secrets, this is misspelled Venemous Tentacula.)

Extended Description
We never find out much about this plant. Professor Sprout knocks its tentacles away in Harry Potter and the Chamber of Secrets. It is commented that people are allowed to swear loudly (in contrast to the silent spell-casting being required for all other courses) in Harry Potter and the Half-Blood Prince if the Tentacula attacks them. During the final battle near the end of Harry Potter and the Deathly Hallows, Neville brings in a Tentacula that grabs a Death Eater and starts reeling him in.

We do see its seeds: small, shriveled black pods that make a faint rattling noise even when they are completely stationary. In Harry Potter and the Order of the Phoenix, Fred and George need these for their Skiving Snackboxes, but they have to get them from Mundungus Fletcher, because they are a Class C Non-Tradeable Substance.