Simple Sentences:
* The disease's insidious spread was barely noticeable at first.
* Rumors of a rebellion were spreading through the city, an insidious threat to the king's power.
* Her smile was insidious, hiding a dark secret.
More Complex Sentences:
* The insidious nature of online misinformation makes it difficult to discern truth from fiction.
* Climate change is an insidious problem, its effects slowly and subtly impacting our planet.
* The politician's lies were insidious, carefully crafted to manipulate public opinion.
* The insidious influence of advertising can subtly shape our desires and choices.
Figurative Language:
* The company's marketing campaign was an insidious worm, slowly infecting consumers' minds.
* The rumors of a ghost haunting the mansion were an insidious whisper, slowly filling the air with fear.
Remember: "Insidious" can be used to describe something that is harmful or dangerous in a subtle and devious way.