These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Of course, anyone who had actually seen Watership Down might have had an idea of exactly what sort of 'movie magic' they were in for... and still been shocked by just how much bleaker The Plague Dogs manages to be.
Nightmare Fuel: Both the novel and the movie are rife with it, but the movie's deleted scene with the mangled and eaten corpse of the Bounty Hunter is probably the worst.
Only the Author Can Save Them Now: More explicitly than most — the book seems about to end with the dogs drowning at sea. The Reader protests and cries out for the Author to spare them, claiming that Real Life would end badly but this isn't Real Life. One Deus ex Machina later, the dogs are saved.
The Woobie: Rowf and Snitter. They are arguably the biggest woobies in the history of fiction, even more than a character like Shinji Ikari, who goes through more mental torture than them. Why? Because they're just dogs who just want a home and someone to take care of them.