Probably needs more greens (chlorophyll) in his diet. Animals get cravings for vitamins & minerals that they lack in their diet. Humans do too, but we think it is for chocolate. 

Love the new Avatar! And I love what you posted here!
I worked at the Long Beach Animal hospital for the 2 yrs. we were stationed there and am fully aware of the fact that chocolate is poision to dogs, they should also not ingest onions, or garlic. You are absolutley correct.
I took if for granted & thought everyone know that chocolate is poisionous to dogs, thank you for pointing that fact out CanMan, heck it may just save some poochie's life:)