On June 24, 1995, at 1000 central daylight time, a Piper PA-18- 90, N5424H, was undamaged while standing with the engine running near Rio Hondo, Texas. The private pilot nor his passenger were injured; however, a bystander on the ground sustained serious injuries. Visual meteorological conditions prevailed for the personal flight. The aircraft was owned by Texas Dusting Services, Rio Hondo, Texas, under 14 CFR Part 91. According to the operator, the pilot hand-propped the engine and was seated in the cockpit waiting for the engine to warm-up prior to taxiing for takeoff for a local flight. The operator added that the pilot asked an employee, who was standing near the midspan of the leading edge of the right wing, to go into the office and retrieve his can of soda. The bystander acknowledge the pilot's request, then proceeded on a course that took her into the path of the turning propeller.