It depends on the type of choc as well as amount the highr the cocoa solids the less u need...the darker the choc the more toxic it would b.
Also a box of chocs...lots will be coated fondents etc so not likely to be fatal. there used to be a saying....it takes a yorkie to kill a yorkie so thats a lot of milk choc for a little dog, wouldnt like to test the theory tho!
Death by chocolate! Sounds like the way to go 4 me