The science behind the pain-free bite from an otherwise unassuming little fish could lead to the development of new painkillers.
The fang blenny, which has two large canine teeth jutting out of its lower jaw, uses its venom to put off potential attackers, rather than to kill its own prey.
But researchers used experiments on lab mice to find that the blenny's venom seems to be painless.
Associate Professor Bryan Fry is from the University of Queensland's School of Biological Sciences Venom Evolution Laboratory and he led the research, along with Dr Nicholas Casewell of the Liverpool School of Tropical Medicine.
Prof Fry said the fang blenny was an "excellent example" of why nature and unique habitats must be protected, particularly the Great Barrier Reef.
The reef is one of the Australian habitats for the fang blenny but warmer ocean temperatures are thought to have caused destructive coral bleaching .
Prof Fry said: "If we lose the Great Barrier Reef, we will lose animals like the fang blenny and its unique venom that could be the source of the next blockbuster painkilling drug."
The fang blenny's venom contains a neuropeptide that occurs in cone snail venom, a lipase similar to one from scorpions, and an opioid peptide.
When a bigger fish eats a blenny, the tiny fish bites the predator's gums.
The bigger fish's blood pressure goes down, it loses coordination and its mouth opens involuntarily, meaning the little prey can swim away.
"The predators would shake and quiver, and open their jaws and gills really wide," Dr Casewell told New Scientist.
"What's more, they never eat blennies again, so whatever the effect is, it seems to be very unpleasant for predators."
Prof Fry said the venom was "chemically unique".
He added: "The venom causes the bitten fish to become slower in movement and dizzy by acting on their opioid receptors.
"To put that into human terms, opioid peptides would be the last thing an elite Olympic swimmer would use as performance-enhancing substances. They would be more likely to drown than win gold."
The research is published in Current Biology.