<p>When a peace officer has to quickly size up a canine as friend or foe, wagging tails don't tell the tale, two experts from American Humane told Tennessee Highway Patrol supervisors yesterday. ''A wagging tale is the worst indicator of aggressiveness,'' said Emily Weiss, who works at the Sedgwick County Zoo in Wichita, Kan., and is an animal behavior consultant for American Humane. The eyes, ears and body are better indicators of whether a dog might bite, Weiss said. In aggressive mode, the whites of a dog's eyes will be more visible, his ears will stand up straight and the body will be tense.</p>