The brown patch on his left shoulder is a result of an odd side effect of his distemper shot.
Soon after the shot, he lost all the fur in that area. When it grew back, it came in looking
like the fur of a Golden Retriever (which is what his mother is). Neither the vet
nor anyone else we've asked seems to know whether it will ever return to normal.
[P.S. (Dec. 2006). It did return to normal within a few months.]