Signs and symptoms of acute peritonitis (rigid abdomen, rebound, fever, severe abdominal pain) immediately following an appendectomy are almost always secondary to intra-abdominal contamination during the procedure resulting in the formation of an intra-abdominal abscess. Surgical site infections usually present less acutely and are milder. Post-surgical bleeding into the abdomen would give peritoneal signs but the patient would be less likely to spike a high fever and would likely present with hypotension. Pulmonary embolism would present as dyspnea and chest pain, rather than abdominal pain.