For many years, conspiracy theorists have claimed that the government conducts top-secret chemical testing in the skies above us. As evidence, they point to "chemtrails" - actually ordinary airplane contrails, or condensation trails - that, it's claimed, have some sinister purpose.
In his conspiracy book "Above Top Secret," Jim Marrs notes that "No one in a position of authority will admit that they exist, much less who is responsible, and what purpose they may serve. Unlike many mysteries, this one is visible to anyone who cares to look up on the days that large jets weave narrow and continuous vapor/chemical trails through the sky."
It's odd that conspiracy theorists are so certain they exist but can't even agree on what, exactly, they are or what they do. Some say it's a sinister government mind-control experiment. Others say the trails are a form of weather control. Still others insist that experimental drugs are being tested on unsuspecting urban populations.
ANALYSIS: Why Do Some Believe Conspiracies at All Costs?