According to the chemtrail conspiracy theory, long-lasting trails left in the sky by high-flying aircraft are chemical or biological agents deliberately sprayed for sinister purposes undisclosed to the general public. Believers in the theory argue that normal contrails dissipate relatively quickly, and contrails that do not dissipate must contain additional substances. These arguments have been dismissed by the scientific community: such trails are simply normal water-based contrails (condensation trails) which are routinely left by high-flying aircraft under certain atmospheric conditions. Although...