* AdaptationDisplacement: Inspired by the book ''The World Without Us'' which, due to its success and also to perhaps because it was named one of ''Time'' Magazine's Books of the Year for 2007, suddenly made this subject very popular. The Magazine/NationalGeographic Channel also had a [[DuelingShows very similar show]] at the same time called ''Aftermath: Population Zero''.
* InferredHolocaust: Not just the humans, but the animals that are bound to die in our absence.
* NauseaFuel: "Last Supper" (Season 2, Episode 4) features a Fort Worth, Texas supermarket that was abandoned for several months in 1999 [[WayPastTheExpirationDate with all the food still inside it]], and goes into great detail about what happens when you leave an entire grocery store's worth of food sitting unattended in the summertime in Texas.[[note]]After complaints from neighbors over the smell, the supermarket was fumigated and stripped to the bare walls.[[/note]]
** Abandoned supermarkets. Especially the meat and deli departments. All that rotting food is going to give nightmares...
** The thought that our precious friends will become vicious hunters. The notion that animals will forget you and humanity in due time. The fact that the smaller and weaker pets, such as toy breeds, will not survive along with some of the more poorly designed breeds.
** Eventually, given millions of years, there will be no trace of evidence that we humans were ever here, save for perhaps some fossils if we get so lucky. All of our achievements, all of our buildings, all of our records now lost and buried with time. Like we never existed in the first place.
** For pet lovers, the pilot episode of the first month or so takes extra care to mention the millions of cats, dogs, hamsters, and fish all locked inside their houses, waiting for humans that will never show up. And then they had to show cats pawing at the doorknob and dogs scratching at loaves of bread, desperate for food.
** Also the RealLife fate of the animals in the New Orleans aquarium, nearly all of which died after Katrina because the facility was evacuated and nobody was there to keep their tanks' water from turning foul with wastes.