Driven by our powerful survival motivation to understand and control the world around us, our brain is congured to interpret available sensory information. The sparse input available in the quiet darkness, therefore, stimulates our brain to make sense of what is available and particularly to draw our attention to any potential threat. Being primed to interpret danger under quiet low-light conditions, taking no chances the brain provides us with a picture that represents potential threat. This powerful “perceptual error” is analogous with those generated by visual geometric illusions, which are anathema to the brain’s need to make sense of the environment. In these cases, it switches between possible interpretations so as to offer us the choice of which to accept as the “true” picture. In cross-modal illusions, such as the ventriloquism or McGurk effects, the brain is similarly driven to produce a credible overall picture of events. Thus, what may be called perceptual errors often reect our attempts to make sense of our immediate environment by maximizing the use of available stimuli with the key motivation being survival or “evolutionary tness.” As information overload narrows the brain’s focus to what it perceives to be most relevant to current performance, the information available from attenuated sensory input will be amplied, and perhaps distorted, to produce a view of the world that makes sense to the perceiver. Thus, what may on one level be construed as errors may need to be understood within a broader adaptive framework.