The slow shutter speed will cause blurness, but when the rear sync kicks in, the flash of light freezes the people at your focal area. Go try it out in a dark room... place some dim lights there and shoot at a slow sync with a slow shutter speed, and move your camera a bit before you aim at a target...
As for the pictures bit, you better apologise to the owner, not me. Just trying to remind you guys about the courtesy bit.