The scene involves an apparently victorious Mami having her head chomped and decapitated by the witchCharlotte's true form. This scene acts as a plot twist due to the first two episodes depicting a typical lighthearted magical girl story, whereas the rest of the story would gradually turn into a gritty dark fantasy.
The general depictions are:
A body hanging in the air with the head out of frame.
Charlotte's mouth is wide open, ready to chomp somebody.
Mami loses or having lost her head, one way or another.
This tag is loosely translated into "Mami chomp", with "mogu mogu" as the onomatopoeia for chewing. The name came from the runes appeared during Charlotte's labyrinth scene.
Because of the nature of this tag, please add the spoilers tag as appropriate.
Verbs of this form may be transitive or intransitive; e.g. 取る is transitive and 判る is intransitive. Both of the Japanese wiki articles cited indicate that マミる is an intransitive verb.
マミられる (Mami-rareru, to be Mami'd; alternate & much less common version)
マミった (Mami-tta, has been Mami'd; past tense of Mamiru)
