Slipping between characters' inner thoughts within a single scene, breaking a fixed point of view.
Head-hopping is unmarked switching between characters' interior perspectives inside one scene - a paragraph in her thoughts, then suddenly his, then the waiter's. It differs from a deliberate omniscient narrator: head-hopping is accidental drift that leaves the reader unsure whose story they're in.
The usual fix is to pick one viewpoint per scene and hold it, breaking to another only at a scene or chapter boundary. What reads as insight into everyone at once actually flattens all of them, because intimacy comes from restriction, not access.
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