Why do animals hide their warning signals? A paradox explained

Scientists have understood quite well why so many poisonous animals have brightly colored bodies - the colors send a message to the predators: " don't eat me, or you'll get sick and die". But why some toxic animals actually hide the warning colors from the predator's view, showing them only at the very last moment, when they are already attacked? How can a sudden display of bright underwings at the moment of capture help a distasteful insect, such like the spotted lanternfly (see Figure and movi