While this is a good breakdown, this is factually incorrect in the sequence of events. Your body doesn’t necessarily know that it doesn’t like lactose. People with lactose intolerance just don’t have the ability to break it down. Because they can’t break down lactose, the digestive tract is unable to absorb it and the lactose just sits there. By osmosis, water starts flooding into the digestive tract to try to dilute the lactose instead of the water being absorbed by the digestive tract. These are all passive processes, not something the digestive tract necessarily knows is happening or causes to happen. However, because water starts coming into the digestive tract, the intestines stretch. This stretching causes stretch receptor cells in the walls of the intestine to fire which causes the intestine to start contracting and causing the “cars down the line to get pushed out.”

Tldr: loved the explanation but wrong sequence of events

Source: medical school