What is the most resilient parasite? Bacteria? A virus? An intestinal worm? An idea.

Inception :-

 "What is the most resilient parasite? Bacteria? A virus? An intestinal worm? An idea. Resilient... highly contagious. Once an idea has taken hold of the brain it's almost impossible to eradicate. An idea that is fully formed - fully understood - that sticks; right in there somewhere."

-Cobb, Inception, 2010