In the Back to the Future trilogy, Doc Brown has a dog named Einstein in the year 1985. Now when Marty goes back to the 50's, he seeks out a thrity year younger Doc Brown, who lives in the same house and owns the same dog as he did in the 80's. Okay, he does call Einstein a different name in 1955 (Capericus), but it is generally implied that he's the same dog. How can that be? The average life expectancy of most dogs is 10-15 years. How could have Einny lived that long?