A 40-year-old male presents with intermittent epigastric pain for 3 years, often occurring when hungry or at night, and relieved by food. Two hours ago, he suddenly developed severe epigastric pain radiating to the entire abdomen, accompanied by profuse sweating. Physical examination reveals abdominal muscle rigidity, generalized tenderness, and rebound tenderness, suggesting possible ulcer perforation. Which of the following signs is most indicative of ulcer perforation?