Cerebus Callback

A specific type of Call Back wherein a previously humorous or light hearted moment in the continuity is called back to and takes on a much harsher tone. For example a previously funny catch phrase will be repeated on someone's deathbed or a light-hearted memory will be referenced, making the memory take on a darker tone.

Compare Cerebus Retcon when a comedy plot element is deconstructed and played straight and Dark Reprise when it's a song. See also Funny Aneurysm Moment for an unintentional version of this. Note that it only counts when the previous moment is actually referenced. When it's a form of dialogue reversal, see Ironic Echo. When the thing being called back to seemed like more of a throwaway than anything, that's Meaningful Echo.

Examples:

 * In Coraline, Mr Bobinski's circus is one of the things that wows Coraline on her second visit and is the sight of some amusing moments. When she looks for the second ghost child's eyes she ends up getting attacked by everything in the circus. And the cute jumping mice turn out to be rats in disguise.
 * In Tangled as  he whispers to Rapunzel "You were my new dream" referencing a light-hearted song from earlier in the film "I've Got A Dream".
 * Also referencing Flynn and Rapunzel's conversation while waiting for the lanterns. When Rapunzel asked what would happen to her after her dream of seeing the lanterns was fulfilled, Flynn answered, "Well, that's the good part, I guess. You get to go find a new dream."
 * During the number "A Guy Like You" in The Hunchback of Notre Dame the gargoyles give Quasimodo the Ace of Hearts card while they're trying to convince him that Esmerelda would love him. Shortly after this when he sees Esmerelda kissing Phoebus, he pulls out the card and rips it up.
 * In Thelma and Louise, Thelma and Louise take a polaroid photo of themselves at the start of their trip and stick it to the rear view mirror in the car. The photo flies off the mirror.
 * In the Angel episode "A Hole In The World" there is a Running Gag early on about the characters arguing on who would win in a fight - cavemen or astronauts. Towards the end of the episode  she whispers "cavemen win, cavemen always win" as a reference to the plot parallel of.
 * The same episode has a light-hearted flashback scene of Fred packing up her things preparing to move to Los Angeles. At the end of the next episode  they show another scene of her waving goodbye to her parents and driving off to Los Angeles.
 * In Suburban Knights, The Nostalgia Critic gives Ma-Ti the "important mission" of getting him a coffee to keep him out of the way. Cue tears.
 * Remember all that funny Becoming the Mask and Critic refusing to get into character? Well,, he rips off his always-present tie while running to him, loses his glasses and looks like he can't bear to wear his full Critic costume when he's depressed at home.
 * In Everyman HYBRID, A Day In The Life was a Breather Episode of sorts, until hidden clips in future videos paint a more sinister tone on the whole day.
 * A Knights Tale has a scene where William first arrives in London, he imagines that a young boy cheering him on is himself as a child. Later on  the same boy runs up to him and slaps him in the face.
 * The Hole has a really dark example. In Liz's version of events the group make up a fake scenario to fool Martyn. The scene is done comically but then.
 * The Breakfast Club has Brian talking about how he failed shop because he couldn't make a ceramic elephant, which leads into a bit of joking on the part of the others. A few minutes later when the entire discussion has gone a bit more dramatic, Brian reveals . It gets subverted when they all end up laughing about it anyway.
 * The group picture the girls in The Descent take of themselves the morning of the caving trip shows up at the end with the credits rolling over it.
 * The Charmed episode "Vaya Con Leos" opens with a humorous scene of Leo trying to persuade Piper to buy an old van. At the end of the episode when  Piper is seen in the garage tearfully looking at the van.