In the first of the two studies, the researchers sought to determine which genes out of about a thousand might still be functioning in zebrafish and mice in the immediate days following death. To their surprise, the researchers found that hundreds of genes sprung back to life. Not only that, the activity of some of these genes actually increased. Most of these genes eventually gave up after about 24 hours, but some remained active for as much as four days after death. That’s surprising, to say the least.

The majority of these zombie genes were not random in terms of function. Each of them play an important role when an animal experiences some kind of trauma or illness. For example, some genes that were ramped up are responsible for stimulating inflammation and the immune system as well as for countering stress. Some genetic activity, like a gene that’s responsible for embryonic development, baffled the scientists. Noble suspects that this gene becomes active because the cellular environment in dead bodies must somehow resemble those found in embryos.