Article in English: When you have checked for hunger, pain, and discomfort, and have soothed your child, she may continue to cry. Sometimes babies just need to cry, especially in the first three months. Normal prolonged crying sounds like ordinary fussy crying. Your baby may be overly stimulated or have excessive energy.  A fantastic resource to help you understand normal prolonged crying is the Period of PURPLE Crying (https://dontshake.org/purple-crying). This program provides materials to help you understand the characteristics of crying in normal, healthy babies. Normal prolonged crying can last up to five hours per day. A baby with colic will cry intensely with no cause. The cry sounds distressed and is often high-pitched. It may sound like your baby's pain cry. Your baby may show signs of physical stress: clenching of the fists, curled up legs, and stomach clenching. Your baby may pass gas or soil his diaper at the end of an episode of colic crying.  Colic crying happens at least three hours per day, more than three days per week, for at least three weeks. Unlike normal prolonged crying, colic crying tends to occur at the same time every day, around the time of normal fussy crying.  Try to keep a diary of when your baby cries and for how long if your baby seems to cry a lot. Talk to your doctor if you are not sure if the crying is due to colic or not. The cause of colic is unknown. There is no proven remedy. Soothe a colicky baby, and hold him upright when nursing to limit stomach gas.  Your baby should not cry from colic after three or four months of age. Colic does not have any lasting ill effects on a baby's health or growth. Some cries may be telling you that something is seriously wrong. An abnormal cry may be very high-pitched, up to three times as high as your baby's normal cry. It may also be unusually low-pitched. A high or low cry that persists may indicate a severe illness. If your infant is crying in a way that sounds strange to you, call a doctor.  If your baby has been dropped or bumped and is crying...

Summary in Vietnamese:
Nhận biết tiếng khóc kéo dài bình thường. Nhận biết tiếng khóc do đau bụng. Nhận biết tiếng khóc bất thường.