Spirama helicina resembling the face of a snake in a deimatic or bluffing display
Deimatic behaviour – Wikipedia
Deimatic behaviour or startle display[1] means any pattern of bluffing behaviour in an animal that lacks strong defences, such as suddenly displaying conspicuous eyespots, to scare off or momentarily distract a predator, thus giving the prey animal an opportunity to escape.[2][3] The term deimatic or dymantic originates from the Greek δειματόω (deimatóo), meaning “to frighten”.[4][5]
Deimatic display occurs in widely separated groups of animals, including moths, butterflies, mantises and phasmids among the insects. In the cephalopods, different species of octopuses,[6] squids, cuttlefish and the paper nautilus are deimatic.
Displays are classified as deimatic or aposematic by the responses of the animals that see them. Where predators are initially startled but learn to eat the displaying prey, the display is classed as deimatic, and the prey is bluffing; where they continue to avoid the prey after tasting it, the display is taken as aposematic, meaning the prey is genuinely distasteful. However, these categories are not necessarily mutually exclusive. It is possible for a behaviour to be both deimatic and aposematic, if it both startles a predator and indicates the presence of anti-predator adaptations.
Vertebrates including several species of frog put on warning displays; some of these species have poison glands. Among the mammals, such displays are often found in species with strong defences, such as in foul-smelling skunks and spiny porcupines. Thus these displays in both frogs and mammals are at least in part aposematic.