I had noticed it before, but never really taken note. When Jack, Kate and Charlie head off to find the cockpit, Vincent is watching them from the bushes. The way the camera pulls back and the music make this a fairly creepy moment and I wondered why they put such a focus on this.
Then I began to wonder, is Vincent really Vincent anymore? Or perhaps, is he sort of reanimated the way Christian seems to be?
In one of the Mobisodes on the Season 4 DVD set Christian and Vincent are together and Christian says something to the effect of, "Go wake up my son. He has work to do." So, if you will accept this as canon, there is a connection between the two of them.
Nikki has a whole sidebar in one of her Finding Lost books about Vincent as the dog of doom. He certainly gets himself connected to many of the happenings on the Island.
Vincent often acts in a very purposeful way. It seems very odd to me that after the crash he takes so long to find his way back to people. He is in the bushes, he is nearby, yet he doesn't do anything to find his master, Walt. For such a friendly dog, he simply watches Kate, Charlie and Jack, he doesn't bound up to meet them as I would think to be more natural. It is almost as though he is biding his time.
We don't know all the rules about life and death on this Island yet, and I will have to continue to keep this in mind as I rewatch, but for now, I definitely have my doubts as to what Vincent really is.