Give an example of two other body systems that work together, and explain how they support each other.

Cardiovascular and Respiratory Systems, The cardiovascular system with its heart-pump and network of arteries and veins shuttles oxygen-rich blood from the lungs to all of the body's organs and tissues. Cells throughout the body take their fill of oxygen and nutrients and dispose of carbon dioxide and waste products, which eventually flow back to the heart's right-sided chambers; then on to the lungs to exchange carbon dioxide with oxygen. Inhaled air passes through your nasal passages, throat and lung airways reaching tiny alveoli, the site of gas exchange. The newly oxygen-rich blood travels back from the lungs to the heart's left-sided chambers, where it gets pumped out at great pressure via arteries to reach the needy tissues once again. And so the cycle continues. Other organ systems, such as the endocrine and nervous system, directly and indirectly regulate the cardiovascular system.  Digestive and Excretory Systems

The digestive system is responsible for breaking down food into molecules small enough to be used by the body's cells and tissues. The food is broken apart through chewing and stomach churning, but also chemically -- through the stomach's acid-loving enzymes, and on to the small intestine, which receives pancreatic enzymes and juices specially tailored to dissolve and digest proteins, carbohydrates and fibers. Bile from the liver also works on fats. Though absorption of some drugs and alcohol may start in the stomach, absorption is mainly the function of the small intestines. Digestible nutrients pass through from the small intestines and their microvilli to capillaries and on to the liver for detoxification and further processing and conditioning, then out to the body.

when you rub, you also apply pressure, that pressure can urge the poop to come out. i think that when your rubbing, you also might be slightly breaking it up and that can further fill the stomach.