Think red means danger? Good, because so do cobras. And for a snake that kills or maims thousands of people a year, it's reassuring to know we're on the same page when it comes to warning signs.

Scientists have found there is a correlation between the colour on the cobra's body and the toxicity of its venom. The brighter the colour – whether it's scarlet or vibrant yellow – the more potent the venom of the cobra.

"The bold bands or bright colours advertise danger and these cobras have higher levels of defensive toxins in their venom than the cobras of more muted colour," said University of Queensland venom expert Bryan Fry. "It's a bit of honesty in nature."

An international team led by Associate Professor Fry has also revealed how the cobra – found in Asia and Africa – got its flesh-eating venom.

Despite their fearsome reputation, cobras are shy creatures and use venom as a plan B in their defence strategy. Venom is deployed, either by biting or spitting, only after the snake's trademark hood has been extended to ward off potential threats.

"The hood serves to make the cobra look bigger," Associate Professor Fry said. "It's like the guy in a bar who puffs up his chest."

But if that doesn't work, the snake will call on its trump card, often with fatal consequences.

It hasn't always been that way. Associate Professor Fry said cobras gained their hoods about 18 million years ago – much earlier than they started to use venom as a warning rather than purely to kill prey.

He said African cobras began to spit their venom about 8 million years ago, while Asian cobras started spitting venom relatively recently – roughly 3 million years ago.

The destructive powers of cobra venom are well known. Some spitting cobras can cause blindness, while those that deliver the venom by biting can leave toxins that eat away at the flesh, often resulting in amputation.

Associate Professor Fry said that because the venom was taxing to produce, the reptile would rather not dispense it unless it really had to. Shying away from confrontation also reduced the risk of injury to the cobra.

The study findings, published in the journal Toxins, could also have implications for human health, with the chemicals found in the venom a potential source of toxins for drug treatments targeting cancerous cells. 

"Anything that kills cells is a good thing, because it could potentially be used to kill cancer cells," Associate Professor Fry said. "Next we are going to purify these toxins into their individual components and test them on healthy and cancerous cells. You never know where the next wonder drug is going to come from - it could be one of these animals that people vilify."