In the realm of horror, monsters are rarely defined for their intelligence. Jason Voorhees may be imposing, but he's as dumb as a bag of hammers. The Blob is unstoppable, but it's probably not going to receive a PhD anytime soon. Although fiends like these are lacking any grey matter, it doesn't stop them from being absolutely terrifying.
That's why it's so much scarier when a beast is able to think and strategise with disturbing efficiency. Being hunted by a brainless creature is frightening, but it's much worse when the monster in question can set up traps, trick their victims, or play elaborate mind games.
Now, the range of intelligence on this list varies tremendously. Some behemoths are reasonably smart, while others could give Einstein a run for his money. But since monsters are usually packing brute strength, advanced technology, or superpowers, any level of intelligence makes the threat they pose far greater.
And since people assume monsters have a low IQ, it makes it easier for the grotesque critters to catch their victims unaware.
Even though the monsters on this list look frightening, it's their mind you should be worried about.
10. The Vines - The Ruins
Contrary to what The Happening depicted, man-killing plants can be frightening. And as has been demonstrated in The Ruins, murderous flowers can be the stuff of nightmares.
After a group of young travellers discover an archaeological dig, they're attacked by locals, forcing them to seek shelter on a Mayan temple. Although they appear to be safe, the gang quickly realise the vines surrounding the ancient structure are far more dangerous than the natives. The vicious vegetation has a nasty habit of burrowing inside anyone who gets too close for comfort, giving them an agonising death.
But that's not the scariest part. Like a parrot, the ferocious flora are capable of mimicking any noise they hear. They repeatedly imitate the sound of a phone ringing to entice the party towards them.
After Stacy has several vines ripped from her body, the flowers whisper, "I need to get it out", convincing her the plants are still inside her. This strategy works, since it compels Stacy to hack herself to death.
Although the vines' tactic is simple, it's heavily effective, since only one member from the group makes it off the temple alive.