Answer: Aunt Edna
After Clark gets pulled over in Colorado, the police officer asks him to get out of the car, and shows him Dinky's (Aunt Edna's dog) leash tied to the rear bumper of the car. Apparently, Clark had forgotten to untie the dog from the bumper before they left the campground earlier that morning. Dinky was dragged along behind the car, causing him to die. When Clark gets back in the car, he is trying his best to lie about the reason the policeman pulled him over, so Aunt Edna won't have a fit. Clark and Ellen try to convince everyone that Clark got pulled over because he was speeding, and that's when Aunt Edna pipes up and makes her comment about Clark exceeding the speed limit for thousands of miles.