47 y/o female PMH appendectomy presents with three days of worsening abdominal pain and constipation. Over the past day she has had persistent vomiting. She appears ill and has a diffusely tender abdomen. You quickly order labs and an obstructive series with upright chest XR with concern for a perforated viscus. To your surprise the CXR shows no signs of air under the diaphragm. Are there other signs of pneumoperitoneum could you look for on abdominal films?