In the first episode of the film trilogy, The Matrix, lead character Neo was given the option of taking a red pill, which would enable him to understand what was actually occurring, outside the illusion created by the Matrix, or a blue pill, which would allow him to return to experiencing only that illusion. Because he chose the red pill, Neo became aware of the oppressive, parasitic nature of the Matrix.
Tierney, Kathleen. 2005. "The Red Pill." In Understanding Katrina: Perspectives from the Social Sciences. New York, NY:Social Science Research Council. (Oct): http://forums.ssrc.org/understandingkatrina/the-red-pill/