The demon proceeds to cast a spell that prevents Twister from telling anyone about this. The spell did not prevent Twister from researching the occult on his own; this is how he finds a way to break the demon's original spell.
The demon cast a spell forbidding Twister from revealing information about it. Nevertheless, Twister was still able to study the occult independently; he discovered a method to break the demon's initial spell by conducting his own research.