Around 15 minutes after a mammal’s brain is cut off from oxygen, the organ is supposed to die.

Without life-giving oxygen, the cells of the brain quickly starve. Some of the cells burst open, while the chemistry of others becomes so imbalanced that their membranes break down. This frenzied spiral ends one way: in death.

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“My first reaction was holy shit,” says Hank Greely, a Stanford law and ethics professor who reviewed the findings and co-authored a commentary on the paper in Nature. “The conventional wisdom is brain cells die, irretrievably, after about 10 to 12 minutes without oxygen — and that’s part of the scientific underpinning for the definition of brain death, the definition of death in humans. The idea [that] after four hours with no oxygen, or glucose, or anything else, most of the cells in the pig’s brain would start functioning again? That’s astounding.”

It’s so astounding, he says, that perhaps we should reconsider the definition of death. And we should definitely consider the unexplored ethical implications of partially reviving a dead animal. Because, what if, even for a moment, that pig brain felt something?

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“I think they’re right, that given the lack of an EEG, it would be shocking if there were any consciousness there,” Greely says. “But are there parts of the pig brain that are somehow sensing and reacting to pain? … [I]s that something to worry about? The lack of an EEG is very comforting, but what comes next? Will there always be the lack of an EEG? … My honest answer to the question of ‘does this make the possibility of reanimation thinkable?’ is ‘maybe.’”

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Greely adds, “We have an obligation not to be cruel to this former pig.”

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In the meantime, Greely and Farahany suggest, the research can continue, but scientists need to keep safeguards — like the neural activity blockers and the anesthesia — in place in the case any consciousness is revived.