 Other common symptoms include intense perceptual disturbance such as visions of insects, snakes, or rats.These may be hallucinations or illusions related to the environment, e.g., patterns on the wallpaper or in the peripheral vision that the patient falsely perceives as a resemblance to the morphology of an insect, and are also associated with tactile hallucinations such as sensations of something crawling on the subject—a phenomenon known as formication.Delirium tremens usually includes extremely intense feelings of "impending doom".