I spoke to the vet and he said pretty much what I thought. It's the root from the milk tooth being reabsorbed. It is loose but, if it doesn't fall out within a month, than I should take him to the vet for further examination. He said that this is when some bad breath can kick in. I have noticed Max's breath becoming a little "off" for lack of better words. He lost three teeth in the last two days - of course - not the brown loose tooth LOL! Poor guy is down to one canine. :)