What do annotation arrows indicate?
Air along the wall of this hollow viscus in right hypochondrium. Probably pneumotosis intestinalis or emphysematous cholecystitis.
to look for free gas under the diaphragm
There is no free gas under the diaphragm. In the right upper quadrant, there is an air-fluid level with a curvilinear lucency visible around the fluid component (see Series 2, annotated).