Because of eating bones, nuts and elastic toys. Intestinal parasites such as ascaris lumbricoides, tapeworms and ascaris ileus in puppies under four months old are the main reasons. Postoperative intestinal adhesion, intestinal tumor. After eating, strenuous activity causes mesentery rupture, septum rupture and umbilical hernia, which causes intestinal tube to enter the rupture hole and hernia ring and cause intestinal atresia. Canine distemper and enteritis can cause partial intestinal paralysis, and the peristalsis of the anterior intestine can be strengthened, which can lead to secondary intussusception.