On July 26, 1994, at 1800 central daylight time, a Cessna 182, N2564R, piloted by the private pilot/registered owner, sustained substantial damage when it ran off the end of Runway 27 during an aborted takeoff at Galt Airport, in Greenwood, Illinois. The private pilot, the certificated flight instructor (CFI) and the one passenger aboard reported no injuries. Visual meteorological conditions prevailed for the flight, no flight plan was filed. The flight operated under 14 CFR Part 91, and originated from Greenwood, Illinois about 1759, with an intended destination of Rockford, Illinois. Both pilots reported the flight was intended as a dual instrument instructional flight. They planned to depart the uncontrolled airport VFR, and practice instrument approaches at the Greater Rockford Airport in Rockford, Illinois. Both pilots stated the airplane preflight inspection and engine run up proceeded normally. The CFI reported nothing unusual was observed until the airplane was about 1/3 down the runway, and "...had not yet begun to lift off....at this point where the plane is usually breaking ground. The airspeed indicator was indicating zero." The private pilot stated he reduced the throttle and began braking to abort the takeoff. The CFI reported she assisted in brake application and keeping the airplane under control. The airplane ran off the departure end of the 3,200 foot runway, continued up a small hill and came to rest in a corn field. Postaccident examination revealed a mud dauber nest blocking the pitot tube. There was no evidence of preimpact mechanical malfunction. Postaccident investigation revealed a pair of heavy black skid marks, approximately 600 feet long, down the runway. The skid marks continued into the grass, up the hill, then disappeared briefly, to reappear in the corn field where the airplane came to rest. The airport manager witnessed the airplane as it ran off the runway, and he estimated its speed to be 40 mph. He stated both pilots were "standing on the brakes, with full power applied, for about 1,000 feet...they finally throttled back near the end of the pavement." A record of telephone conversation is appended.