Like you'd expect from any activity involving green horses, the 100-Day Thoroughbred Challenge offered spectators at the Maryland Horse World Expo, Jan. 18-20 in Timonium, Md., some thrills, spills and surprises. But it also offered inspiration (to ride better), information (on why Thoroughbreds off the track do some of the things they do), and a solid case made on behalf of ex-racers as excellent sport horses-in-waiting.