The stomach expands on inhalation and can feel as though it rolls out to the left.
The stomach is a J shaped, hollow, muscular organ suspended under the diaphragm by folds of the peritoneum. (The gastrosplenic and gastrophrenic ligaments to the diaphragm, it is connected to the liver via the hepatogastric ligament, part of the lesser momentum). The greater omentum attaches to the lower border of the stomach, like an apron trailing down the front of the peritoneum.
The stomach hangs off the liver. It fills much of the space under the left diaphragm. When holding under the left diaphragm the hollow muscular bag can be felt in the anterior portion of the cavity space, above the retroperitoneal pancreas. It feels quite different from the gland like, more active, pancreas and the blood filled bag of the spleen.
Orient to the motility, feel the hollow muscular bag and the surrounding visceral fascia. The stomach should move with the diaphragm and not feel sticky against other structures. The tone of the muscular bag should be evident. Learn the difference between an empty stomach and a full stomach.