Hundreds of buffalo thundered across the Wyoming plains Thursday after news of actress Jenna Elfman's latest sitcom, Accidentally On Purpose, spooked the unsuspecting herbivores. Upon learning of the new CBS comedy about a single woman who finds herself pregnant after a one-night stand with a much younger guy, the buffalo charged en masse, responding as if by instinct alone. 'A stampede of this magnitude is extremely rare,' said Howard Kremer, a specialist in herd-bound behavior who noted that this was one of the most destructive events of its kind he had ever seen. 'Only a large enough threat, such as an approaching pack of wolves, or a quirky prime-time vehicle built around the former costar of Dharma And Greg, could trigger it.' At press time, the frightened herd had run itself off a nearby cliff, so blind was its desire to escape the hijinks and hilarity airing Mondays this fall. 