"That's the heart of the matter"

I have the following problem: I am translating a script, or rather only the titles and the dialog for the subtitles, into English. (I am a native English speaker). I would love it if I could translate "Da liegt der Hund begraben" with "That is where the dog is buried", but I know full well that I would not have understood that if I read it somewhere. On the Internet I have found some sentences with this phrase, but mostly with an explanation following it or in texts illustrating the difficulty of translating idioms!! Indeed it seems to be a favourite example for this problem, which strengthens my believe that it is not correct English...

The problem is: This phrase is first of all the title of the movie. It is also used as the final sentence, concluding a long conversation between 4 characters in which they realize what their problems in life are and they find a common factor, "the heart of the matter". All OK so far, one needn't stick with dogs if that was all, but the problem is that this whole conversation takes place while (!!!) they bury a dog in a wood after it was run over. This is basically the only action in the film, the rest is basically "just" people talking about themselves while smoking grass. (Sounds terrible summarized like that, but actually the script is quite good). Now how on earth do I link this thought of " the heart of the matter" with the dog that is actually being buried, the way it is done in the German??? Any ideas, anybody?? (I would also be thankful for loads of messages proving me wrong that most native speakers would not understand "where the dog is buried"...)I am currently living in Germany, so I can't test it, but maybe some of you in America, Britain etc. can ask some friends who do not have any German knowledge whether they know the phrase "That is where the dog is buried?" ? (Luckily the film will only be subtitled, if I had to find a solution that had to fit the movements of the actor's mouth as well, I would go nuts!)