Different babies have different manifestations of mental retardation. First, in infancy, children with low intelligence often have difficulty feeding, do not suck, and are especially prone to vomiting, which suggests neurological damage and later intellectual impairment. Second, these children may have facial and physical abnormalities, such as congenital dysmorphic children with wide eye spacing, slanted eyes, tongue dragging outside of the mouth, drooling, and delayed motor development, such as crawling, walking, and sitting later than their normal peers, and walking may be more obvious. In this aspect of language development, normal infants imitate pronunciation at 7-8 months, call their father and mother when they are about 1 year old, say about 10 words at 1.5 years old, understand simple instructions, and answer questions simply by about 2 years old. Any time a child is 4-5 months or even 1-2 years behind, he or she must be seen by a specialist at the hospital. These children have relatively poor communicative skills and suffer from severe distraction, poor memory, poor verbal skills, low thinking skills, emotional instability, poor self-control, lack of self-confidence, and difficulty learning to interact and communicate normally among people.