Illusion: An incorrect and distorted perception of something objective. There are many causes of illusions. Poor perceptual conditions, reduced visual and auditory functions, strong emotional influences, imagination, suggestion, and disorders of consciousness can all cause illusions. People who are hard of hearing often mishear what others say; timid people walking at night may mistake trees for human figures, and mistake their footsteps for someone chasing them, etc. The illusion itself does not necessarily indicate a disease, because healthy people can also have illusions, but healthy people are able to reacquaint themselves with them. In pathological states, especially in various degrees of impaired consciousness, often appear illusions. For example, in delirium caused by infection, poisoning or physical illness, the patient may see the clothes hanging on the hanger as ghostly images. But illusions are not always pathological, normal people in fatigue, mental stress, fear and in poor perceptual conditions, but also produce illusions. Such as the Chinese idiom of “cup of bow and snake shadow, grass and wood, etc., just to illustrate the ease of illusion when nervousness, fear. However, the illusions of normal people are generally short-lived and self-correcting. Pathological illusions generally occur in cases of poisoning, infection, etc., mostly visual illusions, often with horrific content. Hallucinations: Patients perceive the existence of something that does not exist in objective reality, such as auditory hallucinations, visual hallucinations, olfactory hallucinations, taste hallucinations, and touch hallucinations. In the case of auditory hallucinations, there is no one around the patient, but the patient hears someone talking or scolding him/her, and the patient believes it and often acts accordingly, such as scolding the “voice” he/she hears. Most hallucinations are pathological and are a common type of psychotic symptom, and patients are often convinced of the phenomenon and content of the hallucination. Therefore, there is a fundamental difference between delusions and hallucinations.