London, April 18 (ANI): The mechanism behind the menacing 'hood flare' which cobras use as a defensive display has been discovered by scientists.

By measuring the electrical activity from the snakes' muscles, researchers discovered the precise group of muscles cobras use to raise their hoods.

According to their study, the cobra's hood evolved as its ribs were 'co-opted' to create the threat display.

"In the cobra, both the [rib bones] and the muscles that work them are deployed to erect this visual display," the BBC quoted study's co-author Kenneth Kardong, professor of zoology from Washington State University in the US, as saying.

"We wanted to examine the way in which the ribs were 'freed up' to rotate into this presentation position, and to understand how the muscles were able to accomplish that and return them to a relaxed position," he added.

For the study, the researchers took measurements of electrical activity from all of the muscles in the cobra's neck.

They had to embark on some very tricky surgery to implant tiny electrodes into the snake's neck muscles, with the animal very carefully anaesthetised.

Once the electrodes were in place, the researchers waited for the snake to recover before filming and recording the muscle activity as the animal flared its neck.

They found that just eight muscles were involved in 'hooding' and that they were muscles that were also present in non-hooding snakes.

"This is an example of evolution's remodelling [as] derived species emerge. There's been a change in the nervous system's control over these muscles," Kardong said.

The findings have been reported in the Journal of Experimental Biology. (ANI)