This installation enables a live plant to control a machete. plant machete has a control system that reads and utilizes the electrical noises found in a live philodendron. The system uses an open source micro-controller connected to the plant to read varying resistance signals across the plant’s leaves. Using custom software, these signals are mapped in real-time to the movements of the joints of the industrial robot holding a machete. In this way, the movements of the machete are determined based on input from the plant. Essentially the plant is the brain of the robot controlling the machete determining how it swings, jabs, slices and interacts in space.

(Via David Bowen's plant machete.)

Science fiction writers don't spend a lot of time writing about violent plants, but I do recall this instance from one of my favorite novels, Doorways in the Sand (1976) by the remarkable (and much missed) Roger Zelazny. Dr. Mrmm'mrm'mlrr (pronounced just like it looks) is a sentient (and telepathic) psychotherapist plant who practices assault therapy on his patients.

As the cablelike vines or tentacles seized me, thigh and shoulder, hoisting me into the air to a position where, wrenching my neck, I was afforded a view of the thing's massive trunk, down to where it emerged from the tub of slime in the center of the room, I reflected, as the enormous Venus-flytrap-type blades snapped open, revealing a reddish interior, that while it may be true that most accidents are caused by carelessness, I could in no way be held responsible this time...

I struggled, of course. Who wouldn't? But the thing raised me a good five feet into the air, shifting me into a horizontal position directly above its less than attractive self. It then proceeded to turn me upside down, so that my field of vision was dominated by its gray-green bulk, its tub of slime and its octopal members all awrithe. I had a hunch it meant me ill even before its leafy appendages came open like switchblades, showing me their moist, spiny and suspiciously ruddy insides.

I let out a bleat and tore at the vines. Then something that felt like a red-hot poker occurred behind my eyes and passed from side to side and back within my head. Stark terror poured forth, and I twisted convulsively within the living bonds...

Most of us remember the delightfully chaotic and violently deciduous Whomping Willow from Harry Potter and the Prisoner of Azkaban (1999), but you might not know about the predatory gum tree from Symbiotica (1943) by Eric Frank Russell:

With a mighty swoosh a branch above his head drove down. Its spatulate leaf smacked him squarely in the back and a waft of pineapple and cinnamon went all over the place. Just as swiftly, the branch went up, carrying Jepson high into the air. Swearing like a tail mechanic, he struggled furiously while we gathered below him. He was stuck to the underside of that great leaf, gradually became covered in thick, yellowy-green goo as he writhed...

('Predatory Gum Tree' from Symbiotica by Eric Frank Russell)