'It all started with their difference in philosophy over health care reform,' said Senior Deputy Eric Buschow of the Ventura County Sheriff's Department. The incident occurred about 7 p.m. Wednesday at a demonstration organized by affiliates of the activist group MoveOn.org, which drew supporters of President Barack Obama's health care plan, Buschow said. The rally also attracted several counter-protesters, he said. During the rally, two men got into a heated argument and began fighting. 'At which point, one man bit off the left pinkie of the other,' Buschow said. The injured demonstrator then drove himself to a hospital, he said. 'We're still trying to figure out who was the aggressor,' Buschow said. Ilyse Hogue, director of political advocacy and communications for MoveOn.org, called the incident 'a regrettable act of violence' in a statement released Thursday morning. 'While we do not have any more facts about what happened than what we saw in press accounts, MoveOn condemns violence in all forms,' Hogue said. 'We support the Ventura County sheriff's investigation into the situation. It is in our firm hope that this event does not detract from the tens of thousands who were out peacefully making their voices heard for health care reform and a public option.' 