The foureye butterflyfish gets its name from a large dark spot on the rear portion of each side of the body. This spot is surrounded by a brilliant white ring, resembling an eyespot. A black vertical bar on the head runs through the true eye, making it hard to see. This can result in a predator thinking the fish is bigger than it is, and confusing the back end with the front end. The butterflyfish's first instinct when threatened is to flee, putting the false eyespot closer to the predator than the head. Most predators aim for the eyes, and this false eyespot tricks the predator into believing that the fish will flee tail first. When escape is not possible, the butterflyfish will sometimes turn to face its aggressor, head lowered and spines fully erect, like a bull about to charge. This may serve to intimidate the other animal or may remind the predator that the butterflyfish is too spiny to make a comfortable meal. The psychedelic "Synchiropus splendidus" (right) is not easily seen due to its bottom-feeding habit and its small size, reaching only about 6 cm. It feeds primarily on small crustaceans and other invertebrates, and is popular in the aquarium trade. Just as some prey species evolved cryptic colouration and patterns to help avoid predators, some ambush predators evolved camouflage that lets them ambush their prey. The tassled scorpionfish is an ambush predator that looks like part of a sea floor encrusted with coral and algae. It lies in wait on the sea floor for crustaceans and small fish, such as gobies, to pass by. Another ambush predator is the striated frogfish (right). They lie on the bottom and wave a conspicuous worm-like lure strategically attached above their mouth. Normally about 10 cm (4 in) long, they can also inflate themselves like puffers. Gobies avoid predators by tucking themselves into coral crevices or partly burying themselves in sand. They continually scan for predators with eyes that swivel independently. The camouflage of the tassled scorpionfish can prevent gobies from seeing them until it's too late. The clown triggerfish has strong jaws for crushing and eating sea urchins, crustaceans and hard-shell molluscs. Its ventral (lower) surface has large, white spots on a dark background, and its dorsal (upper) surface has black spots on yellow. This is a form of countershading: from below, the white spots look like the lighted surface of the water above; and from above, the fish blends more with the coral reef below.