Alice is a Sealed Evil in a Can. Bob, either because he was promised something like immortality or riches, thinks he can control her, or because he thinks Alice isn't as evil as everyone says she is, tries to free her. After a bit of hard work, and possibly some outmaneuvering of people with more common sense, Bob frees Alice. However, rather than rewarding Bob for his service or even giving him a simple thank you, Alice tosses Bob into her mouth and eats him without a second thought.
This trope when somebody frees or summons a Sealed Evil in a Can, and is immediately eaten by said evil. Often a trope that appears at the climax of a story. A sub-trope of Evil Is Not a Toy and a common fate of cultists summoning an Eldritch Abomination. One of the hazards of calling up what you can't put down. It's also a sub-trope of You Have Outlived Your Usefulness.
- This happens to Samantha the necromancer in episode 3 of Soul Eater when she summons Wrath of the Pharaoh, because of all his undead subjects, of whom she'd taken control by that point.
- In The Bartimaeus Trilogy, it's generally stated that demons will attempt to eat their summoners if they fail to draw a proper pentagram or stray outside it. Bartimaeus himself alludes to having eaten a few wizards who made silly mistakes in the past. In book two, a wizard is eaten by a demon because he copied the summoning circle from a book whose printer had deliberately drawn it wrong in revenge for the wizard assaulting and crippling his son years earlier in the prologue.
- In The Belgariad and Malloreon by David Eddings, this is a common fate of Demon-summoning sorcerers. The sorcerer can only maintain control of a summoned demon by continuously forcing it into a shape he controls, correcting deviations with more magic. If he gets it wrong, he gets eaten, generally followed shortly by everyone else in the vicinity.
- In The Last Battle, Shift uses the humans' fear of Tash to increase his own wealth and fame. This involves posing as Tash's high priest/chosen one and constantly threatening to sic Tash on Shift's enemies. The real Tash eventually learns about this, and he is not impressed.
Tash: Here I am. What hast thou to say?
- The advice given in The Case of Charles Dexter Ward
I say to you againe, doe not call up Any that you cannot put downe; by the Which I mean, Any that can in Turne call up somewhat against you, whereby your Powerfullest Devices may not be of use. Ask of the Lesser, lest the Greater shall not wish to answer, and shall commande more than you.
- In Pathfinder, Daemons stand out among Evil-aligned Outsiders as Omnicidal Maniacs that will immediately try to devour their summoners, body and soul, and usually continue to try even if they get roped into a Magically Binding Contract. While Devils will try to ruin their summoners with bargains and Demons encourage For the Evulz-style debasement, Daemons just want all life to end.
- Magic: The Gathering invokes this trope via Feaster of Fools, a Demon that has both Convoke (meaning that your other creatures can help you summon Feaster of Fools) and Devour (meaning Feaster of Fools can eat your other creatures when summoned to get stronger, which most likely will be the same people that Convoked it).
DCI Ruling: "[Feaster of Fools] can devour creatures that convoked it, and those creatures can reflect upon the wisdom of convoking a demon."
- In Dark Cloud, once the Dark Genie is free, it eats the person who organized the ceremony. The creature justifies this by saying that it hadn't eaten in 400 years and was hungry.
- In the finale of Mega Man Battle Network 3: White and Blue, Lord Wily's consciousness (he pulled a Brain Uploading earlier) is consumed by the Psycho Prototype Internet that he awakened and unleashed on NetSociety, Alpha.
- A staple of The Unspeakable Vault (of Doom) is Cthulhoo eating cultists that just summoned him.
Cthulhoo: Yum yum!