Morgan going down to the pit where the bodies of the dead are being burnt, looking for the bodies of his wife and daughter.
Morgan opening the door, resulting in his undead wife coming after him, thirsting for his blood. And it's depicted from Morgan's POV.
Whatever the virus was that wiped out humanity, it left behind no bodies. Thus it completely deconstructed them, leaving no physical evidence they ever existed. The only description of the symptoms implies the violent expulsion of blood from literally every orifice. Imagine how horrifying it must have been, knowing the only people who'll remember you are likely going to die the same terrifying way. It must have been worse for the survivors, seeing their friends and loved ones just dissolving into nothing before them, afraid it'll happen to them as well.
Averted in Malibu with the whale carcasses.
Crosses into the Funny zone when Carol shows Phil her roommates skeleton. When Phil recoils in disgust, Carol mentions her roommate was a med student.
Dead human bodies (in the form of skeletons) are seen in a season 2 episode during a scene at a morgue. It is unknown whether they died as a result of the virus, however.
The episode "Pitch Black" finally settles the question. According to Pat, a lot of people died in their homes, many others went to government-designated containment areas where the bodies were either disposed of or put in body bags. A small number survived for a short time and straggled off into the wilderness to die. He also suggests that there are survivors living in underground bunkers, but this is implied to be only a paranoid conspiracy theory.
Proven right with the reveal of Pamela.
Absolutely everything about Mike's situation.
Especially that he has the descent/escape module, but not the training to use it.
In "Pitch Black", he meets a new survivor named Pat. While definitely a little crazy, he seems nice enough. Then when Mike insists on looking for other survivors, he snaps and almost kills him.
"Smart and Stupid" has Mike coughing up blood. Then in the nighttime, the calf's mother dies from the virus.
"30 Years of Science Down the Tubes" Melissa guesses (incorrectly, as revealed in Season 3) that the person who was flying the drone is not friendly. At the end of the episode, Gail asks Todd and Erica to confirm if there is a boat outside. Tandy sees that there is a group of survivors (the above mentioned Pat being among them) on the boat who are armed and heading towards them.
Phil trying to stay sane for two years without any human interaction is heartbreaking as it is scary.
A major one, the nuclear power plant near their home has a meltdown. This is one of the times that Tandy is not acting like his usual self. The worst part is how they find out almost every part of the United States has a nuclear power plant that will eventually have a meltdown.
In season three, "Karl" is another episode devoted to a single survivor of the virus, a la Kristen Wiig's character. The twist? Fred Armisen guest-stars as a cannibalistic serial killer. Some humorous moments come from his dorky personality, but everything else is nightmarish, especially when he meets up with the main cast in the next episode, fighting his cannibalistic urges. Meanwhile, Jasper, A CHILD, is missing. It doesn't seem likely that Jasper and Karl interacted, but even the mere fact that a child is lost in a post-apocalyptic world is so, so disturbing.