The reason is the frantic dog! When UFOs are close by, dogs often become extremely agitated. This would also suggest that there may already be visitors on the ground. It is often true that a close sighting like this is accompanied by ground activities of various kinds. We will try to contact the poster of this video.
http://www.youtube.com/watch?v=9vYxTW6GfFo&feature=player_embeddedStory Source:
http://www.youtube.com/watch?v=9vYxTW6GfFo&feature=player_embedded