From Warhammer 40,000, the reaction of anyone, opposing player or in-universe soldier, to seeing a Chaos Champion being possessed by a Greater Daemon. Described in a few places in the background. One text box sidebar in either the Chaos Marines or Chaos Daemons Codex describes an Eldar autarch's reaction to seeing a Slaaneshi Champion being possessed by a Greater Daemon; his initial reaction is to resign himself to die fighting, but then its magic takes over and he stands there staring at it as it eviscerates him.
Also, when the Imperium tacticians were trying to figure out how the Tyranid fleet was appearing at random locations far too quickly, and then realized that the tyranid fleet was not coming at the galaxy from the edge, but from below the galaxy. You can see one single fleet's attack movements here (remember that this is one fleet, the Tyranids likely have thousands).
Any time a particularly powerful unit does anything, really. Especially if it's something like Drazhar and a band of Incubi declaring a charge.
The Warhammer Fantasy Wood Elves army book has a picture of Naestra, Arahan, and their dragon staring down a Dwarven Slayer, who has a priceless "Holy S***!" look on his face.
Exalted: It's been made explicit that this is going to be the general Yozi reaction to Heresy charms. When an Infernal creates "Swallowing the Scorpion" and snaps the tethers linking his shard to Lillun, the Phylactery-Womb will scream in pain - and it's around that point that Malfeas, the Demon City, literallyshits bricks.
