As a family show that airs pre-watershed, there's only so much violence, death, bad language, and other mature content that Doctor Who can get away with.
You can have a man being mauled to death by a werewolf... but only if it happens offscreen. You can have a group of aliens being sprayed with a machine gun... but only if there's no blood and guts. You can have characters commit genocide... but you can't show millions of innocent people burning to death as their planet explodes.
To put it another way, most of the horrible stuff in Doctor Who is implied rather than shown, and as a result, there are tons of episodes in the modern series that are quite a lot darker than you might initially think.
Whether it's a disturbing moment that is heavily signposted but remains unseen, or even something dark that will likely happen after the end of an episode, the Whoniverse is certainly a pretty grim place to be. But depending on how much each episode shows us, you might not realise just how grim it truly is.
10. The Flesh Feels The Pain Of Amy's Death (The Almost People)
Series 6 introduced programmable matter called Flesh, which was used to create "gangers" - exact duplicates (including memories) of humans.
This raised a major philosophical debate in the first half of the series: should the Flesh be treated as a real, living thing? Or is it simply a disposable tool? There are arguments on both sides, but during the two-part story The Rebel Flesh/The Almost People, it's made abundantly clear that we should all be on team Flesh.
This is because the entire point of these episodes is to show that the Flesh has a sentience of its own, and that it feels pain and suffering when its gangers are "decommissioned" - or, to put it bluntly, killed.
Bearing this in mind then, there's quite a dark edge to The Almost People's climactic TARDIS scene that a lot of people might have missed.
Here - in a shock twist - it's revealed that Amy is a ganger when the Doctor melts her down into a puddle of goop. The real Amy is safe and unharmed, but hang on: didn't we just spend two episodes learning that the Flesh has its own consciousness, that it's alive, and that it can recall the deaths of its gangers?
Most viewers were so blown away by the twist that they probably didn't consider this, but everything we know about the Flesh implies that it will feel the pain of ganger-Amy's death, which effectively means that the Doctor is committing murder with this act.