Humans usually experience rigor mortis – the stiffening of the body – hours after they have died. But that doesn’t seem to be the case with all organisms.

In a study published in Cell Reports, scientists from University College London (UCL) and Washington University found that a small roundworm called Caenorhabditis elegans (C. elegans) actually experienced rigor mortis before it had officially died.

"Cell death has been widely studied but much less is known about death of whole organisms, how it happens, what triggers it, and when it begins and ends,” Professor David Gems from UCL, who led the researchers, said in a statement.

“But it's extremely important for understanding fatal diseases in humans, especially those caused by ageing."

Death is defined in medical terms as the moment that the heart stops beating or the brain stops working. However, there are normally quite a few events that happen before and after someone dies, including rigor mortis.

In C. elegans, which grows to just a millimeter in length, the team found that dying cells trigger the death of neighboring cells through the release of calcium. This starts in the muscle, which is what initiates rigor mortis in the worm. The cell death is described as spreading through the worm “like a house burning down”, according to lead author Dr Evgeniy Galimov from UCL.

^{A video of the process in action. David Gems, UCL}

The reason for the difference from humans is that these worms don’t have a circulatory system to get oxygen to breathe. This means they don’t die from circulatory failure, as happens in mammals. What’s more, C. elegans experienced a “belly punch” when the death of cells in its head drove its pharynx towards its intestine, causing the chain reaction of cell death.

Aside from just being rather interesting, the study could help us understand more about the process of death. In particular, it could shed light on how cells lose the ability to generate energy as they age and lose their ability to hold calcium in the muscles.

"Discovering rigor mortis in worms is exciting as it highlights a key step in the chain of events leading from healthy adulthood to death from old age,” added Professor Gems.

“It helps us to understand death in humans, and perhaps in the future to prevent death in mortally ill patients."